Change your Corbett into attack. There is no downside and as far as I know there is no specific buff for "specialized type" yet. and you can change it back anytime with not cost, no downside, no nothing.

Both Isogiku are good. Isogiku Easter is just mostly unkillable. She pretty much soloed one of the hardest Castle floor (lvl120 I guess) with just Habranthus backup (who died very early anway). She won with more than 100% HP but it was a fail though. Empty slots in a team count as dead girls in the final point calculation. But she did it.
Isogiku Formal is better as support for sure. And she would works very well with herself.