Bows and knuckles are going to be the most common "sub-optimal" weapon types, almost surely. 2-handed weapons are a lot more desirable when you can't inherited Two-Handed for basically free, and more damage is generally more desirable than the modest defense boosts that the average class gets from a shield.
Well, unless you allow the elemental immunity shields via rare steals.
I said swords/spears since a lot of classes get B/A or so ranks in those two and they're pretty strong onehanders that don't sacrifice durability. Bows also may work out, though a lot of classes I suspect may not actually find those to be usable. Ditto knuckles. Good ranks in those are rare and ranks matter immensely. (This also doesn't matter much for me, I'd hod jobs to their top two ranks but) but lemme check...
Classes with bad shield ranks that have theoretical physical use:
Thief: Goes bows, but has an A there so that's not unexpected.
Merchant: Bows C, Spears S: bows outdamage spear+shield, but not by major amounts and Bloody Shield is pretty powerful. Wash?
Red Mage: Sword A, Bows C: Bows will more solidly outdamage here, Sword A won't outcompete Spears S. Bow's valid for RM here.
Salvemaker: Uh if you don't allow offense items, Bow B is their best option for actually doing anything. But if you allow specials, they probably go staves for the super? idk.
Performer: Uhhh, hum. Not sure what the best storebought fist is, it may outdo A Sword, though. Bows look to be a bit weaker for them.
Conjurer: Probably goes knuckles or bows, yes.
so yeah I guess you have a point, bows/knuckles are probably best for some of these people esp. Red Mage so it has an actual offense.
Re: items, yeah, I'd actually probably limit Salvemaker to spending 15k (about average over all boss fights using them, I'd guess? some fights higher in which I shadowflared, some fights lower in which I didn't need much item/healing) so they'd get 2x shadowflare at best. Merchant I'd say 22k thanks to More Money, so.
While I'm thinking about it:
Specials: Require performing certain actions X times. Basically high damage + some stat buff listed that lasts until the song ends (four rounds, less if you're doing Brave shenanigans since the song plays through menu options - I'd say three turns), occasionally elemental/slay (creature)/status. Matters rarely in a duel, but so everyone has a compiled list (I'm referencing a FAQ for this):
Sword: Brave 10/20/30 times. Possibly decent for Spell Blade, who can use drain sword to keep durability up. Otherwise won't likely see use.
Rank 1: ST, PDef -25% down on target, Hit # up +20% on allies. Hits 5 times for 0.6 average phys damage/hit.
Rank 2: MT, +35% PAtk allies, hits for 2x average phys dam.
Rank 3: ST, +50% PAtk allies, hits for 6x average phys dam.
Axe: Kill 5/10/15 enemies with physicals. This will never see duel use unless you allow people to enter with a special prepped (I definitely wouldn't)
Rank 1: MT, +20% PDef allies, hits for 1.5x average physdam.
Rank 2: ST, +35% hit #, 5 hits for 0.8x average damage per hit
Rank 3: ST, +50% PDef allies, hits for 6x damage, base earth elemental
Spear: Deal physical damage to 10/20/30 enemies. Slow in a duel but may occasionally get used.
Rank 1: ST, +300% crit rate allies, hits for 3x average phys damage.
Rank 2: ST, +35% PAtk allies, hits 6 times for 0.6x average damage, has a chance to paralyze (unsure on odds).
Rank 3: MT, +50% PAtk allies, hits for 5x average damage, fire element.
Rod: Cast magic 10/20/30 times. It's another option for BMs and RMs, I guess.
Rank 1: ST, +20% MAtk allies, hits for 1.5x average damage (does this use MAtk?).
Rank 2: MT, +35% MAtk allies, enemies debuffed -15% PAtk/MAtk/PDef/MDef for 4 turns. No damage. (1)
Rank 3: MT, +50% MAtk allies, hits for 5x average damage (does this use MAtk?). Gets an added *150% (so 7.5x) against demon type enemies.
Staff: Heal 10/20/30 times. Items work for this, so it's a Salvemaker option, and other classes with minor healing can find a way to use this.
Rank 1: +100% Healing Magic effectiveness, Heals all allies. At endgame it's still basically a fullheal (6-7k to 5k HP), though that may scale with Norende options allowed. (2)
Rank 2: +35% Speed all allies, buffs all allies +25% PAtk/MAtk/PDef/MDef for 4 turns. (3)
Rank 3: ST damage, +50% MAtk allies, hits for 7x average damage (does this use MAtk? Pretty sure not but), gets an added *150% (so 10.5x) vers. Undead.
Knife: Use 5/10/15 items. Only Salvemaker would wind up having access to this, if anyone, and their physical offense is horrific. Still, for the record:
Rank 1: ST, +20% hit # all allies, hits 5 times at 0.7x damage each.
Rank 2: ST, +35% hit # all allies, hits 15 times at 0.3x damage each.
Rank 3: ST, +50% hit # all allies, hits 10 times at 0.7x damage each.
Bow: Hit elemental/species weakness on 5/10/15 enemies. No elemental bows exist IIRC, and Rangers don't get a slay human option, so this really won't see use.
Rank 1: ST, +300% crit rate allies, 3x phys damage.
Rank 2: ST, +35% hit # allies, hits 5 times at 0.8x damage each, fire elemental.
Rank 3: MT, +50% MDef allies, 3x phys damage, light elemental.
Katana: Default 5/10/15 times. This is a legit option if allowed, and probably the most prevalent special that could see use outside of staff.
Rank 1: ST, +20% PAtk allies, 2x phys damage, inflicts paralyze (low odds?).
Rank 2: MT, +900% crit chance (!) allies, 2x phys damage, water element.
Rank 3: ST, +50% speed allies, hits 5 times at 1.2x damage each.
Knuckles: Critical 3/6/9 times. This... isn't that easy to build up if only due to the inconsistent crit rate. Still, Monks may appreciate it.
Rank 1: ST, +20% PAtk allies, 3x phys damage
Rank 2: ST, +35% hit # allies, hits 16 times for 0.3x damage each.
Rank 3: ST, +50% PAtk allies, 5x damage, lightning element.
Finally, these can all be customized. Any that deal damage to enemies (everything except Staff 1/2 and Rod 2) can be given up to 150% additional damage, an element of choice, the option of slaying a monster type of choice (-NOT- Humanoid), and the ability to try and inflict a status of choice. This can all be done simultaneously (can't choose two monster types or two elements, etc, but can have one of each category simultaneously)
The first staff ability can have additional healing, status curing (any status in game), MP healing, and BP healing (of up to 2 points per use). Very, very handy for WM, as it lets them basically healtank even harder through enemy offense if needed and give a few extra turns. Again, this can all be on simultaneously.
The second staff ability can buff PAtk/MAtk/PDef/MDef/Speed/Evade/Crit% further, give a status resistance effect, give an element resist effect, and have the duration of all this (except the Speed buff) enhanced by up to 5 turns.
The second rod ability can debuff PAtk/MAtk/PDef/MDef/Speed/Accuracy, debuff status resistance, make an enemy element-weak, and have the duration of all this (except the MAtk buff) extended for up to 5 turns.
I'm providing this for a better idea of what's doable with the specials for informed decisions. Many won't even see DL use; staves/katanas/swords will have the most consistent ones, but since the cast is on average going to be good at blitzing and bad with protracted battles, even they won't be common.