"I mean... I guess. Probably. If we managed to fight off an invasion, a whole world probably could."

Assuming that whole world had magic or powerful weapons. Hadriel's kind of cheating, like every other person is a wizard or something.

Of course, the invasion force they fought was somewhat smaller than intended, since Fear moved the city before they could all swarm in. A whole world of Null against a whole world of other people? Might be a more even match.