My theory is similar to this. The sage was stronger that the Jubbi, in order to seal him. He probably had a different dojutsu or non at all before he fused with the jubbi. Because of the negative power the jubbi made the sage weaker after sealing it. Thus naruto will be stronger than madara if he unlocks the sages power without the help of having the rinnegan.Naruto might get it on his own ( chances are low, but still) We don't know how SO6P got his rinnegan. If he awoke it after becoming Juubi Jin, then there's a slight possibility for Naruto too, now that he has chakra from all 9 beasts.