Lol, I actually read your post, and you're an idiot. Especially when it got down to Nagato and Obito.
Concerning Obito, its basically a 4 round fight.
First you have to deal with 6 Edo Bijuus who have shared vision and can predict your movements. Then you have to deal with their tailed beast forms. Then you have to fight a Gedo Mazo. After that, you have to deal with a 100% Obito with Rinnegan, Izanagi and his S/T technique which Itachi has no counter to.
Given Itachi's chakra levels, he probably won't get past the 6 Edo Bijuus.