That makes it even more vulnerable to disruption... If you cast Protection first, and it gets countered, you just... don't cast this. If you cast this first, your entire board gets exiled (and it presumably also gets countered, or someone just floats a white and Swords to Plowshares it once it resolves).

Really, that alone is the biggest reason to change it, not because that's too powerful, but because I think if I was at a table and someone exiled everyone's permanents and then didn't win the game on the spot (or present a foolproof path to victory in a turn or two), I'd never play with them again.