That's a tricky question to answer. The canonical power of the Voice is immense. The Greybeards were able to shake the ground of Skyrim simply by calling the Dragonborn's name. Heck, by whispering it, not shouting. But The Nerevarine is clearly no slouch.  At the same time, there's the unconfirmed matter of whether the Hero of Kvatch became Sheogorath after the events of The Shivering Isles. So, for now, let's just agree that every protagonist is OP.