Cleared the new Proud and Proud+. Much easier than Gilbert IMO since there's no "punishment" for using skills and the boss doesn't become unmanageable by giving itself a ridiculous amount of buffs and doing stronger moves if it has too many buffs/not enough debuffs. There's also no "instant death" moves/attacks like Gilbert, but you have to be aware of it casting Stoned and Zombified on the whole party so you will need veil and clarity sources (ex: Lily, Katalina). And the boss has charge diamonds so delay and gravity works here (Drang, Feower, etc...). There's probably way more ways to clear both Proud and Proud+ than Gilbert in terms of characters/skill options.
The only "trick" this boss has is when you use summons. The boss changes the second unremovable buff to a different version (Attack, Defense, Special) on the same turn if you use a summon vs a set number of turns, and gets rid of one debuff on the same turn. The different forms cause it to do different style attacks/gives itself different buffs (Attack buffs, defense buffs, etc...). So you may want to manage this in terms of not summoning into a form you don't want too quickly or forcing it to move to a different form. Regardless nothing as bad as Gilbert's "restrictions" on certain skills.