I absolutely think that some implementation of this would definitely work. If your title was written as: “What if certain bullets dealt % Max HP damage?”, then people would be a lot more down with this. But I thought it was OBVIOUS that these shots would be far and few in between and not EVERY SHOT IN THE GAME would follow this rule.
You’d have your normal shots, your armor piercing shots that fuck over DEF, and then these HP Based shots that fuck over HP. It’d honestly be really great as I’ve always said “what’s the point of not building health in a permadeath? especially when DEF is considerably worse in almost every regard?”
It would make DEF better by comparison, and put less value on HP users (and no, it wouldn’t make HP useless; that’s never going to fucking happen if pets still exist), which is overall much healthier (pun not intended) for the game. It doesn’t even have to show up much at all, maybe if it was more dungeon gimmicky, or sort of an endgame exclusive type of thing.
Definitely something needed in RotMG. HP is broken as fuck, and DEF is not even close to as good as HP (you’re wrong if you think otherwise (and no, the 1% of situations where DEF is superior doesn’t make the stat better as a whole)), so this would be a nerf to the tankiness of players, and it would add more skill for swapping items out (like back when people actually had 3 rings on hand to swap around for maximum effectiveness).