So, I disagree with you, Alfred, regarding his devil axe change. In fact, I implemented an identical devil axe based on the one that appeared in FE7if.
That being said, I don't like either one compared to my ideal devil axe, but I'll explain.
Original: 50 Hitrate, 20 MT, 20 WT, 31-LUK chance to backfire. This has a LOT of luck variance factors. Not only can it easily miss entirely (Which is at least good for building wlvls safely!) but it also has a backfire chance.
My Devil Axe: 120 Hitrate, 25 MT, 25 WT, 30-LUK rate to backfire. I originally changed the devil axe so it was less luck based. Since it was basically guaranteed to hit, and basically guaranteed to deal a shitload of damage, the only luck-based element here is the backfire chance, which I made possible to negate entirely via having 30 LUK. This is a pretty good implementation.
My Ideal Devil Axe: 120 Hitrate, 25 MT, 25 WT, Does not backfire, but drains 1 max life every time the user attacks with it. Becomes unusable when the user is at 1 max life.
My ideal implementation would allow the axe to still exact a grievous penalty on the user, but one that might be worth the guaranteed huge damage it deals. It's OP, as strong as an S-rank weapon, but not luck based at all, which makes it the ideal solution. I've never seen anyone suggest a better idea than my implementation that Brendor made, so I think this is the best solution to the Devil Axe Dilemma.