We speak of who wins a 1v1 fight, not about what someone did in his past.Itachi < Nagato.
You are overrating Itachi. He couldn't be compared to Nagato. It's simple, can Itachi did what Nagato did to Konoha? Itachi is far below Nagato!
What is fact? It took 3 people Naruto, Killer Bee and Itachi to beat him.
It was only that Itachi had Totsuka Blade and Nagato had leg injuries.
Nagato has no counter for Totsuka&Yata.
GG