J-man had a response for every attack he got thrown at him and he basicly handled every pain and defeated them with the fact that they had way more of an advantage then nagato would because of their mobility and sight from diff angles. If jman knew where he was or if nagato would of fought him man to man i believe nagato would be defeated or in the least they would both die. Especialy if he would of fought him man to man, jman has tons of experience and wouldnt do the same stupid things naruto and bee did.