We already have the benefit of plot armor. We don't need the additional invincibility clause that would come along with the 100%. Be it takes long to charge or not it still just adds another layer of power we would have over hero npc's in this game. Likewise even if I do consider this they also get healed when invincible on top of their over charge.

I'll let you add that feature as 'hero gear' to keep up with patients but I still believe that having that as in innate part of the quirk is a bit much on top of everything. Keep in kind the quirks in my hero are extremely one dimensional and don't often have a lot of facets unless it directly is a part of said quirk like the blood types of that one villain who's name is escaping me as a i type this.