Pain said that Jiraiya would have won if finding out his secret earlier. Finding out his secret doesn't make Pain weaker, but it would mean that Jiraiya could meet Nagato, who is bound to his machine and is unable to fight. In fact, Jiraiya lost against Pain, though latter wasn't using his whole power. Also Naruto, who perfected the Senninmode, was inferior to Pain, fought him in a long scene while Devas abilities weren't present and kissed the floor pretty quickly after Devas power returned. Deva alone soloed Naruto along with his boss summons and Fukasaku.
The thing about Nagato is that his abilities are COMPLETELY DIFFERENT THAN ANY OTHER NINJA. That's what's important about the whole "finding out his secret" deal, not the fact that Nagato in his wheelchair-thing is a seemingly easy target. Jiraiya lost against Pein because he let his guard down after he *thought* he'd won the battle.
Base Jiraiya >>>>>> Base Naruto. Even Imperfect Sage Mode Jiraiya is >>>> Sage Naruto (though to a lesser degree), for MANY reasons.
He is far more dangerous in taijutsu. He doesn't run out of Sage Mode (thanks, shoulder toads!). He has more varied and battlefield-changing ninjutsu. He has two OTHER Perfect Sages on his shoulders, who can offer advice and distractions for the opponents, as well as having their own, powerful abilities. Things like Shima's tongue (her hellish, demonic tongue!), Fukasaku's water jutsu (he can
bisect boss summons!), their potential for combination ninjutsu and the EXTREMELY dangerous Toad Song. He is immune to genjutsu which don't take out Fukasaku and Shima at the same time, immune to Sharingan genjutsu as he doesn't need to open his eyes to "see" the opponent (like Kabuto). He can predict even MUCH faster opponent's moves, much like in Naruto's battle against the Third Raikage.
There's even the argument that not being a Perfect Sage might grant MORE powerful attacks on its own, at least when the problem is TOO MUCH natural chakra, as the only difference seems to be appearance, a slight anatomical change Jiraiya has long since learned to compensate for, and the danger of turning into a toad. Having MORE natural chakra than is safe to use (like SM Naruto
doesn't) might just add to the magnitude of Kawazu Kumite and offer more energy to enhance ninjutsu at once.
Deva Path is VERY well suited to fighting large monsters, like boss summons and the Kyuubi. How odd, that the Rinnegan's most powerful ability would be suited to fighting things like the Juubi.
Deva is much less effective against smaller, more mobile foes.
