Idea:
Make it so defense gives you grey hp while base hp stays green, normal attacks have to go through the grey hp first, but if you have AP a % of the damage you deal goes directly towards the base hp (if base hp reaches 0 you die, obviously)
This could also add some variety in PVE I think, we could have some enemies with much lower base hp but high defense hp
Bigger issue at hand is the lack of resistance and armor piercing haters
Insanity and drawback are bad but they are good at that. Insanity causes some visual effects that may hinder your performance, while drawback forces you to be efficient with your fights.
Resistance and armor piercing are supposed to be good but they fucking suck.