I feel like it'd be a cop out if the staffs did nothing at all to them though, perhaps it just takes a lot of hits for the effect.
I dunno, I feel like staffs that can easily do things of that effect, like change the boss into a lesser mob or whatever, should instead do damage. It would kinda be similar to Maya's ability in Borderlands 2, where enemies such as bosses don't get affected by her paralyzing effect, and instead take an increased amount of damage from it.
And making the staffs just take a certain amount of hits to do their effect would kinda suck. Yeah, I could take this Ocarina, or Bow, etc etc. But why would I take any of those if I can just have this staff that will make any boss fight a cake walk? I understand that if you have an easier/better weapon to use, obviously you would use it. But I feel as if that would make it a bit too easy, boss fight wise.
tl;dr those staffs should do either damage against bosses, not take a certain amount of hits to take effect on bosses, or if they do, make it so that they are rarer