I'm not sure what would be more detrimental in combat, though; -20% max health or -50% damage resistance. I may be mistaken, but it seems that the latter option penalizes the character even harder, while lacking the former one's sense of urgency and need.
Besides, wouldn't the +1 attribute bonus suffer from the same problems as the +20% health bonus: namely, wouldn't it wear off before it can come into play while you're exploring or talking to other characters?
... and please, if anyone from Larian is reading this, keep the Soul Devourer ability. :D
/sorry for the misspellings, I'm trying my best to get rid of them.