I’m against mechanics that render entire characters useless permanently. Like, having a unit sit at 1HP for the rest of the game is a bit… huh. It sure works as a high risk-high reward weapon, but it can also be misused by naive players and that would compromise their whole save file forever. It’s too big of a punishment than just, say, having to reset your chapter and get back the character you just lost.
I don’t like the luck-based backfire either, because the player can just reset the chapter or load a savefile to get a different result. It’s not skill based, and you don’t even need any planning/problem solving skills because you can just get a different result doing exactly the same moves. In the end you only get an OP weapon which is very easily exploited.
tl;dr I dislike the concept as a whole, but I can understand where you guys are coming from and I accept that. We can have different opinions while still respecting each other after all.
P.S. Imo the best solution to the Devil Axe dilemma is to not have Devil weapons at all.
Or let them do something else instead. Like, being effective against staff users, while giving the character a stat penalty if they’re equipped.