I don't get the limitation. Imo it should work with m2 aswell, would make it much more viable.
I think main concern is billy and huntress.
I wouldn't mind it working with m2s though.
Also dark devotion should not have a timer, as it is that perk is really useless.
Its a bug,just like MoM,some hits just dont get registred as basic attacks.
But would it make Billy and Huntress insanely strong? I doubt it tho. I would like to test that in a PTB tbh.
And for example Bubba is weak anyway, that perk working in his m2 would be really great to slug as bubba