I like MaxHP drain being available to players... but I'm not sure I'm fond of it being used like this. It isn't that I mind it working so much as I don't like it when a tedious method becomes the optimum one, because that makes the tedium mandatory which is... not fun.
Not sure what a good answer here is yet.
Enemies don't really have a way to earn experience, so the main player method doesn't work so well for them.
Pure stones... in theory I could train AIs to use items and give them pure stones/gems, but this is just extending the tedium, not eliminating the problem (this would cause other issues too, such as status conditions suddenly becoming very hard to use )
I could have demons attempt to flee the level if they have lowered and the player seems to be kiting... but I'm not sure I like this either.
Hmm. I'll think about it some more.