Two of the new classes, Clockwork Soldier and Arachne, address the gameplay issue of combat classes running out of juice after one or two big moves, and this may well lead to some overpowered combos.
The Soldier Shell draws upon its occupant's HP to refill its combat meter each turn, and has access to the occupant's Combat skills... so stick Nuan in one (even if she absolutely hates it judging by her Flirt text), have her expend some HP on stacking self-barriers (which do not take up her turn), and then Shirogiri to steal all that HP back from a boss. Then she can cast Kurogiri every turn (Soldier Shells have unimpressive AGI so Flame Dance won't land many hits), or even Aogiri instead if there are multiple targets. Probably don't want to use Akagiri, or the shell's power draw will empty her out on the next turn.
Of course, you could instead exploit the "refill Combat to 100 every turn" property to have Annie do some potentially hilarious things with Showdown, though I haven't put as much thought into that one yet. And there's the boring-but-practical choice of just spamming Protect every turn, as Soldier Shelled allies flatout don't die at 0 HP (they just stop being able to refill Combat so quickly)
I haven't played around very much with the Arachne class, mostly due to how difficult it is to get one (you need to make one from a cocooned ally, and I forgot where to buy the cocooning spell tome to do it easily...) Arachnes use other coccooned allies, even ones outside the active four party slots, as Combat batteries. She can just drink the Lust gauge right out of one to fill her Combat gauge without using up her turn. (Another use for the Commoner!) Presumably, this too can allow Nuan or Annie to spam big stuff.
Sable's kind of in shambles since I think the Fellacian Guard class can teach some of her skills to other characters, much like Copy Princess does for Lilina and the new Student class explicitly does for Sinian-- and I'm not sure Sable has enough unique stuff to still merit a party slot like the actual Lilina and Sinian do. Guess we could still just use her as Commoner 2, Commoner Harder.