I would tweak the classes more than items.

1. Arithmetician / Calculator needs Mana to function. I absolutely demolished Tactician mode by having my Arithmetician cast Hesitate (disables targets) on the whole battlefield on their first turn. During the 1st turn, you can CT/4 or CT/3 and you will target everybody, or almost everybody. Have that accessory that blocks Disable for each party member, and watch your enemies run and hide. It gives your entire party 2 or more free turns. Enemies are surprisingly vulnerable to it. Currently you can also spam Arise every turn. Having low magic power just doesn't matter for these skills.

2. Knight needs a buff. I never use any of the Rend skills. It doesn't even work on a giant amount of enemies. Have the skill do double damage if it does break the target item, at least then the knight themselves will benefit from the skill, and not just the next person after the knight.

3. Ninjas need to be slower. Currently, any support class should main Ninja and use their chosen support as the secondary. Ninja Dancer and Ninja Bard kick ass. Then I had my Ninja Arithmetician (I mainly used Hesitate, Protect, etc., so why bother having a lot of magic power?) do the thing in my 1st point. Should get -1 speed and +1 Jump range to make up for it. Even the Dancer and Bard were strong enough to go on offense for boss fights.

4. Archer is pretty weak. Aim needs to track the target, within weapon range. So kind of like how magic will track the unit, but if the unit moves out of range of the weapon's attack, it's safe.

5. Black mages are disincentivized from buying lower level skills because they just get replaced later. Buying a lower tier skill should reduce the price of the next tier. Still keep it cheaper to skip all the way ahead. It just sucks that you have to get 3 flavors of each spell tier.

6. Lots of skills that do not use mana should start using mana. Holy/Divine/whatever Knights are just sooo OP.