A lot of the people named really only start drawing use from it really late
-Yuri 1 for example...starts at L3s, I think?
-Priest...might take several floors to get the MP to use Holy twice?
-CT is one of those games where I believe the characters get much less efficient on MP? On a similar note then, Mana Khemia. But again, for games like this, they are much more damage efficient early.
-Naoto's pretty efficient minus damage, which is...not good. Ironically, if I was using her for damage in dungeon, Blight, which hits HP, would probably be the superior choice because P4 Poison is great and the damage differential is not really a big deal because Naoto's damage is bad regardless (Not to mention Megidolaon would be double the HP cost)
So I think it's a cute idea, I just don't see a lot of use for it in practice (Probably because dungeon is about neutralizing enemies so quickly. Running out of MP might be an issue, but taking all that extra damage or needing to have someone heal even if the enemies did nothing would be a far worse issue). I understand that some people might gain a benefit from it at points, but generally they don't like it enough early. Especially since certainly I'd imagine that the cost being incurred after any healing would be the sane balancing measure.