Yes, Weapon Guard primarily through spillover is the idea.
You can even pretty easily get guest spillover if you already have Move+1 and Gained JP Up on everyone who wants it. Gafgarion and Agrias are a-ok with being Knights. (Chemist is the other obvious Guest Spillover choice if you're done with Squire spillover, but you can't really get Gaf/Agrias guns without taking guns away from Mustadio, so that's a big power drop. Rafa, on the other hand, I'll make Rafa a Chemist all day).
-Well Wave Fist should really be mentioned for Monk. 60 ranged damage probably keeps them off the "painful" list, at least as much as it does Archer (who has less damage but more range/move).
Oh,
trained Monk is fine. Not like...super good or anything, but passable. Trained monk is like...slightly better than untrained Chemist! Maybe!
Partially trained Monk (with just Wave Fist but not Earth Slash) is still fine.
Wave Fist is a 300 JP ability, though. Like...if you're a Ninja, and you're grabbing Martial Arts on your way through, you will never actually learn Wave Fist.
If you're a Samurai, and you're not interested in HP Restore, then sure, you'll have Wave Fist for about half the time you're getting 550 Monk JP.
-Priest is obviously better than many of the random leftover classes, and may even compete for that 5-6 slot. They do only slightly less damage than other fighters, have decent enough MA/MP for magic secondaries, and Cure alone is a cooler skillset than most others at this point (it's great economy if you can AoE it effectively, in particular). I'd certainly value it above Haste, though TM's +1 MA may make them slightly better anyway... still, it's competitive.
Hm, interesting...
I mean...Haste, if you hit 4-5 people with it, and there's a lot of flat ground to do so...
On clocktick 19, with 14 CT, your speed becomes 9. 10 clockticks later, on clocktick 29, you get your second turn. Enemies who move-acted get their second turn on clocktick 34 (you can bolt 2 them a second time). Enemies who move-waited get their second turn on clocktick 30 (ok, yeah, that's bad). If you can manage to drop a spell on the enemies without moving, and also be in the haste, though, then you're....34 CT when haste starts on clocktick 19, which gives you your second turn on clocktick 27...NOPE, that's not fast enough to cast spells on move-wait enemies either.
Certainly if you're a physical setup though (Knight, Thief, whatever) getting hasted round 1 lets you attack twice before any opponent gets their second round. This might mean not bunching up as much for haste, though.
Hm, yeah, maybe I'm overestimating haste.
That said, Priest numbers aren't great.
15 physical damage is...not much different from any other class at this point, but nevertheless still game-lowest.
34 healing with Cure (assuming your party has 70 faith across the board) is nice AoE healing. I still wouldn't set it as a secondary over Potion+Phoenix Down on a Wizard, though--Wizards run out of MP. (And on all other mage classes, Black Magic).
29 damage with Bolt. Yeah, not bad. Less than all the other mage classes (47 on Wizard, 41 on Oracle and Summoner, 35 on Time Mage).
I guess my biggest issue is that I'm not entirely sure the reason why you'd be in Priest in the first place. Knight you might be on the way to Samurai or Ninja, you might be picking up Equip Sword. You might just be chilling long enough in Knight to get all your mages Weapon Guard. You might be Delita. Time Mage you might be on the way to Summoner, and Time Magic secondary (with just haste learned) is an acceptable skillset on physical classes like Archer, Knight, Thief, etc, cause it mostly ignores MA and Haste is really good if you aren't worried about lining up CTs. You might also be in Time Mage 'cause you want Teleport or will eventually want Short Charge.
But like...what's the motivation to be in Priest in the first place? There's no rush to get Holy for chapter 2...or really any Priest ability at all. I guess if you're en-route to Calc, then yeah, might as well do your Priest levels in Chapter 1, cause Priest gets worse in Chapter 2.
But sure, you can and do multiclass between all the mages fairly easily, cause they all have robes, decent stats, and you only need 50-200 JP to have a decent skillset for multiclassing. Priest has the worst stats in Chapter 1 (but not too bad), catastrophically terrible stats in Chapter 2, and actually pretty good stats in Chapter 3 where the extra point of speed is pretty nice.
Don't get me wrong, if Auto Potion was a Priest ability I would learn it way more often. Priest is a lot nicer to be in than Chemist. But like...if we're going there, Oracle can use Thunder Rods and has more MA, and thus is probably nicer to be in than Priest at this point (and certainly nicer in Chapter 2).
I'm trying to figure out what I'm actually trying to say here hmm.... Well...I guess mages are pretty spoiled. All of them have both "pretty good stats" and "abilities I want to learn". Priests having both the worst earlygame stats and the fewest abilites I want to train towards for Chapter 2 makes them...frequently get passed over for me I guess? At this point in the game, anyhow. (They pick up again in Chapter 3/4).