So I just had an idea, what if weapons that we've taken from our enemies (like Lord of Wolves, Anarchy, Acrius, etc) received increased ammo drop chance from the enemies the weapon is themed around? Like Acrius would get more from defeating cabal using it, LoW from defeating Fallen, Div from defeating Vex perhaps...
I think it would be a unique way to add another special thing to these weapons that may encourage their usage in PvE