You're very smart, aren't you? It required an equal team-work of the 3 to beat Nagato, and not just that, but Naruto went all-out against Nagato, just like the other 2. Itachi took-out Nagato with Amaterasu, and then he came back with Shinra Tensei; Naruto wasn't able to do that, which proves your theory wrong. They were all going all-out.
PS: I bet that other account is your alt and you wrote that to yourself.
Maybe Killer Bee was equal to Itachi but Naruto was not. You said they fought even with him but he also got KA'd as soon as he activated MS so he didn't use his most powerful techniques on them.