I'm bored at work, so I figure I may as well throw in my 2 cents. Here's how I'm going to gauge the classes.
1) I don't assume that this is hardcore min-max world where Math Skill has beaten the game by the start of C3. While I'm going to give Math Skill some credit for its capability to reduce every fight to a single ability, the truth of the matter is that is not how most people play FFT. It's a little difficult to articulate this because this is ranking jobs on their effectiveness at beating the game, but it also assumes that you aren't setting up your entire party to optimize/synergize the way a CT5 Holy strategy demands. IOWs, there is some fun factor being weighed in where the more degenerate/boring a strategy is, the more I'll squint at giving it credit. People simply enjoy blowing up their enemies with giant space rocks and/or angry thunder gods, or punching demonic blobs and goats for absurd damage, in a way that watching Holy cast 10 times in a row as the only fight interaction doesn't provide.
2) Jobs are not ranked SCC-style or in a vacuum. Synergy with other jobs (and how easy it is to achieve said synergies) are definitely taken into consideration.
3) The amount of time investment (JP grind, generally), and overall the efficiency of the job, is a strong factor that is weighed as heavily, if not more heavily, than end/aftergame value which assume an overabundance of JP.
4) The difficulty of execution is factored in somewhat, but generally assumes a player is well-versed in FFT. This mostly is some wiggle room for CT calculations, Teleport, etc.
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1. Summoner
Minimal investment: Easy to unlock. Early summons are absurdly damaging, efficient, and handily destroy the game. At 4 CT it is kind of really hard to mess Ramuh up even late.
Overall endgame value: Does technically get supplanted by Math Skill. But the rest of their skillset remains relevant (run your big summon of choice for assassinations, Golem is great utility, Moogle is solid healing, etc.) and you'll almost certainly never feel lacking in options nor power using Summon.
2. Wizard
Minimal investment: Coast on Bolt early on, grab Magic AttackUP later. Utterly wrecks the first two chapters due to stats and abundance of magic boosting equipment.
Endgame value: Best carrier in the game for the top skillsets, Summon and Math Skill. There isn't much that a Wizard with Black/Summon doesn't rip to the ground effortlessly for pretty much the whole game. Also the best user of Draw Out in the aftergame if desired.
3. Chemist
Minimal investment: 90 JP for better than half of the skillsets in the game. The immediate assumed default secondary for everyone early on, and probably still always set on at least one PC for the guaranteed, easy revival. Auto Potion is the best reaction in the game and comes at a dirt cheap 400 JP relative to its power.
Endgame value: Phoenix Down only gets better the longer the game goes. Auto Potion remains overpowered from start to finish. They simply don't provide any offense in a game where killing everything quickly is generally more efficient, but they are amazing at making sure you don't reset due to silliness or random mistakes.
4. Squire
Minimal investment: All that guest JP spillover and time you spend in Ubersquire is so hard...
Endgame value: Yeah, this is all up in that Gained JP Up and Move+1. Yes, this is so utterly prevalent that they place this high despite basically being ignored past C1 otherwise. Footnote - I recognize that Gained JP Up technically lets you access the good broken stuff (Summon mainly) faster, but past that delay it doesn't really matter too much because you don't actually -need- that much JP to break the game over your knee. Past that point it's just mostly for fun and playing with variety for the sake of variety. Which is all fine and good, of course, but is the main reason I have it below Chemist.
5. Calculator
Minimal investment: I'm always a bit surprised at how tame Calculator's unlocks are relative to its potential. They're pretty much equivalent to Ninja and Samurai, and makes Mime even more sad.
Endgame value: Newsflash, Math Skill is still insanely good even when you don't optimize your entire party for it. It is kinda painful to grind up Calc JP but it doesn't take -that- long and doesn't take a lot of spells for it to be really, really good, either. The sheer variety and power that the skillset presents is undeniable, on top of being instant and free.
6. Ninja
Minimal investment: In pretty much no way, I think, does Ninja even touch Calculator for effectiveness as the other usable late-unlocked job in the grand scheme of things. But on the other hand, Ninja is great out of the gate and needs less grind overall.
Endgame value: It gets perhaps more credit than it objectively deserves by being one of the few actual viable physical options in FFT. Still though, gamebest speed and OHKOs are things no one ever passes up, and it does edge out the mage jobs in some fights where going first and killing something immediately is helpful.
7. Time Mage
Minimal investment: Haste is nice, although it does present some additional difficulties to those using spellcasters. Demi is often overlooked despite it being a fairly easy to grab boss killer (I dunno, it just isn't that exciting). They suffer a bit from being pretty much all utility, which doesn't actually end fights. But overall they're a well designed job where everything feels usable and impactful - can't really go wrong with hasting your team and slowing the enemies and such.
Endgame value: Teleport rocks, of course. Short Charge is really more of a way to play around with most of FFT's spells to make them bearable rather than coming down to use the few insanely broken ones (see: Ramuh, Bolt) except for the Meteor setup, which does of course crush a large segment of the game if you're up for it.
8. Priest
Minimal investment: I'm honestly not at all impressed by Priest as a healer. Item is way, way, WAY better early on... like it's not even close - Potion and PD cost less than any two abilities on Priest, are instant, cheap, and just generally far more effective (don't need to worry about faith, cast time, etc.) Raise is kinda nice despite these drawbacks because it returns targets with HP but I still don't feel it comes close. Cure is good as inexpensive MT healing, but this is FFT - you're usually better off just killing stuff before it hurts you. By the way this is what Holy does.
Endgame value: 600 JP to put your faith in the light. The steam engine for Math Skill's omnipotence. Still great as an assassination spell on Wizard or whatever. It is pricy, but you don't normally need to cast it more than once. They also have speed which can be kinda nice sometimes if you need to sync up with enemy speed on a mage class.
9. Oracle
Minimal investment: Most people I know make Paralyze or Sleep the go-to spell on Oracle when they first pick it up. It's easy to see why, as they are strong debilitating spells with some aoe that just make a problem go away. Silence Song is amazing when it is relevant. Life Drain is fast and kills zodiacs dead. Sticks are cool, though honestly not that great IMO.
Endgame value: Most of it's up in Life Drain, I think, although again people don't tend to run 'Life Drain x4 to end the fight right away' unless they're doing a challenge or something. Otherwise, Oracle is a bit awkward because status just ends up being less efficient and slower than blowing things up in FFT, and that's the rest of their skillset (I mean, I am ranking the trio of Cure/Raise/Holy above all of YYM, which is kind of harsh but I think is actually true in practice). A lot of it just isn't accurate enough to be worth using or investing in. However, it is still an FFT mage, and thus is better than every other physical job not named Ninja.
10. Mediator
Minimal investment: Comparisons to Oracle are obvious. On the other hand, Invite can be absurd, they don't have charge times and they don't need to worry about faith. They're also gun users and can use Black Robe + elemental guns, which is nice. But their skillset is pretty much a two-trick pony (Invite, Mimic Daravon) aside from...
Endgame value: Br/Fa twinking. It's there, it's a thing. It's not really ever necessary and serves more to deal with OCD compulsions to perfect your party members, I think. They do certainly offer more than Oracles with dedicated use but I'm pretty sure I'd take an Oracle over one in just generally playing through the game.
11. Geomancer
Minimal investment: You only actually need a few Elementals for the skillset to be decent. You don't ever set it, but hey, you're not using Geomancer for its skillset anyway. Obviously a solid carrier for Agrias (much, MUCH better than Knight IMO, at least pre-Excalibur) and Attack UP pretty much cements this.
Endgame value: If Agrias didn't exist and wasn't so popular, Geomancer would be so much farther down the list. I mean, -yeah-, they can be mage carriers with 4 move and shields, thanks to Rune Blade/Aegis/etc. but I don't actually think these benefits, nice as they are, really can beat out the far more obvious carrier, Wizard, which comes with native Bolt and just way more damage. But I appreciate that they exist as an option, nonetheless.
12. Monk
Minimal investment: WHY ARE MONKS 3 MOVE. I remember mc saying over and over how much this aspect of them was making her cry when we were playtesting them in LFT. An interesting and varied skillset - said variety having a lot of appeal and making Monk quite popular with new FFT players, I find - hampered by being overpriced in JP costs, having annoying vertical tolerance issues, and being rather ineffective by the time you do actually buy them, with one notable exception (Earth Slash).
Endgame value: Earth Slash is indeed quite good, though pricy. Hamedo has... uses, though it's still just way too expensive. No hats is of course an utter killer in a game where hats give you the god stat, speed. Martial Arts Ninja is a thing. I had a very hard time trying to decide whether Punch Art or Jump win out when mastered, but Monk's just more fun. And yeah, Martial Arts Ninja edges them out for me.
13. Lancer
Minimal investment: Yeah, they're kinda eh... 3 move again (why), not fast, armored class. But hey, spears are all right (beat out swords for a good while, the extra range makes up for the mobility somewhat; they're pretty underrated).
Endgame value: Mastered Jump is good and definitely competing for best physical skillset. It's just really boring.
14. Knight
Minimal investment: Weapon Guard! Kinda usable in C1 if you aren't Bolting everything to death for... some reason! And generally everyone will have Knight unlocked, unlike some other jobs (hi Thief), because FFT magic/physical sides of the job tree are ~balanced~.
Endgame value: Well there are better reactions, like I don't know, Auto Potion over there. Admittedly RSM tend to be a bit of the backburner so you may end up just using a freebie Weapon Guard for quite same time, and it's all right at that. Excalibur can make one work sorta maybe. But otherwise, uh, why would you, ever, terrible skillset, terrible equipment, ugh.
15. Samurai
Minimal investment: It isn't.
Endgame value: I like Draw Out a LOT design-wise. But I pretty much have to echo NEB on this: it is forcibly staggered progression, expensive gil wise, expensive JP wise, the job itself is terrible on stats and equipment, and no one here has bought Blade Grasp hype for over a decade. In the super lategame department why on earth would you run this over Math Skill, objectively, other than because it's less time consuming to click through the abilities? If you throw out Math Skill and really don't want to worry about charge times then sure, it's a thing and it's pretty cool... strong self-centered MT damage, healing, buffs, and an 8 range nuke that supercedes every damaging DO before it (<_< >_>). How popular it seems to be with players is a testament that they had a good idea here going, but botched pricing it way too much.
16. Thief
Minimal investment: You get Move+2 when you go to Ninja! Steal Heart is cheap and usable, easily the best (the only?) skill they have available.
Endgame value: I have approximately zero respect for stealing shenanigans as a serious exercise because of the absurd timesink. You do it if you want to be a collector, but that's really about it. Everyone knows how bad they are otherwise. So they're a Ninja engine and little else.
17. Archer
Minimal investment: There is literally nothing here worth looking at that isn't Concentrate. Oh my god, Charge is so bad (yes yes I know you can make it work a bit early on but why would you stay in this job beyond the JP you need for Concentrate is beyond me.)
Endgame value: Concentrate's cool on your Ninja. But Move+2 is guaranteed and Concentrate isn't. Bows were cool at Dorter 1 when that enemy Archer was wrecking your shit with his Longbow, and then quickly become irrelevant.
18. Bard
19. Dancer
20. Mime
Too lazy to explain these in-depth, but they're pretty obvious (way too late, don't do enough being that late. Bard has comedy option Move+3 for those who don't like Teleport and it's easier to JP grind with them. Both have some okay early abilities in Life/Angel Song and Nameless Dance, but meh.)
Redeeming Mime is the reason I made LFT.