Pain said himself that he wouldve lost if Jiraiya knew about his powers earlier. If Jiraiya had beaten Pain then that would invariably mean that Jiraiya could beat Nagato. And where are the pages hailing Nagato as the Second Sage of 6 path's. I would like to see them since I don't remember reading anything about that. Even if Nagato were healthy he still would've lost to Naruto and his talk/book no jutsu. Nagato just doesn't have a warrior's mentality or a true peacekeeper so he is weaker than the war-lover(Madara) and war-suppressor(Hashirama).
LOL
Underrating Nagato again.
Just because he said him in his Paths would've lost, doesn't mean him in his full power would've lost.
When he's in his Paths, his power is Split into 6 bodies, which makes him weaker. If full-power Nagato faced Jiraya alone, it'd be Overkill.
All his Paths are in 6 bodies, which means each body can only do one thing.
You can face each of those bodies, with all knowledge about them, 1 on 1 & beat them.
When Nagato has full power, which means he is controlling all the powers in one body will make him extremely powerful. That's 6 God-Like powers, all put into one Person. DESTRUCTION.