allow me to rephrase that. Im not going to consider anybody on Rikudo Sennin level until the level mountains/cities with a swipe of their hand. Nagato has an arsenal himself. If Kabuto uses unkillable edo tensei, nagato responds with unkillable cerberus and the unblockable shinra tensei and chakra disruption blades that cut through anything.
I never was discounting edo's. but I am saying that there are ways to combat edo's in a more efficient way. there are some ninja who DONT need an army to win. Kabuto is in the top 10 easily, that is why he is one of the final protagonists. But he is in no way comparable to the rikudo sennin when he himself would be slaughtered in an instant by his juubi chakra, gedo mazo, or sacred tools.