In a game where you can dodge attacks 2x damage makes a lot more sense than 2x health. They could also just increase game speed by 10-20% to make everything more chaotic. More enemies + more drops also works pretty well IMO but a sponge just makes everything take sooooo long. RPGs already often have long battles that can take 10 minutes and making the 20 where you use up all consumables, ammo etc is just bad.