He was fighting Chojuro, Mizukage makes it sound like he was Kage level at that time. In fact the whole point of that fight was for Chojuro to take the next step into becoming stronger, and when he did it was gg.
The moment White Mask Obito decided to fight he did the same, and that was without doing a single rinnegan technique.
Bro I think you're overrating Nagato by a lot;
Here's Hanzo casually escaping soul dragon
Obito can easily Kamui away if a basic body flicker can just dodge this attack, Nagato would also risk gimping his body if he dares to use this technique.
Nagato also has a shit reaction time compared to Obito, look at how easily Itachi caught him:
Obito is the guy who according to Minato could match FTG. In fact, Minato said if Obito would catch him offguard it was gg.
I'm sorry but it really comes down to Kamui soloes.