Here is why I agree Naruto will become the strongest. "Will." I do not believe Naruto as of manga 580, is the strongest Ninja warrior.
Okay let's Start off with the Original Sage of 6th path. Legend says he appeared out of know where, he had the body, and the eyes (rinnegan right) He fought the 10 tailed beast, and became the first Jinchuuriki. Right? However, I am a little lost on why he no longer existed, because he had all that power, and "the body." Also some statements of people having the body live long lives, and other things that speaks of immortality. This idea that I am about to say, is a little extreme, I know that. But it said one person will become the sage, a deity of god, which was the original one, and by all knowledge Gods do not die, right? So if the first Sage of sixth is a God, did he really die?
Anyways, I'm only stating this because how "Tobi" comes into play. How this Person knows so mucha bout everything, and he seems to predict many things. I think he purposely set up Minato to make Naruto a Jinchuuriki. I think he has been making plans to make people into The sage of Sixth Path. That is why legend says they can be truly evil sages, or truly bless. I think he is trying to find the one to bring ultimate peace. Which is in fact his main goal in his plan to create eternal peace. However, this maybe a scheme just to bring fourth destruction, turmoil, and to eventually weed out everyone, until he finds the strongest suitor, which is probably deemed Naruto.
I only say this, because Legend said Madara unlocked Rinnegan before he died, he died because he didn't have the body, or chakra to sustain the ocular power of Rinnegan, that is why he died, or possibly used a last resort jutsu to temporarily put his body in a vessel "zetsu" in order to eventually get a new body that can give him what he wants.
That last sentence conflicts with the idea of the original sage finding a new Sage to bring peace. SO Actually I'm saying Tobi might be a Sage or some force trying create a new Predecessor, or it could really be Madara who became the Second sage of Sixth Path but died because he didn't have the body. SO he is on a hunt to find a worth body??? Which he may have weeded out to be Naruto. I also say this, because There was a Quote by Madara saying, that he feels alone in the world, and he doesn't understand a lot of things, but he felt like he has to fix the world all by himself, which is why he wants to have the sage body, which he needs Naruto, and use all the 9 tails beast to make the 10 and become that Jinchuuriki.
I say that, also because when he visited Nagato, and said look your hair became white, he used too much chakra, and his Uzumaki body wasn't strong enough. Also Nagato isn't a Jinchuuriki like Naruto, this making Naruto having a stronger body, and have higher Chakra level.
However, also Remember when Naruto talked, and helped Son Goku. By doing all this, it Showed how Naruto truly is different. He has the will, the body, also is a Jinchuuriki. These are all facts so far. I think he is eventually is going to have all the Tailed on his side, and I think they will all lend him their powers. Which is different from the Original Sage who fought them and became the Jinchuuriki. That is why Naruto is going to be better than the Original Sage, be being able to have Peace with The 9 tails, or making them back into the 10 tailed, and taming that, and becoming the sage?
I think that this is Possible, I mean the Manga is Called Naruto for a reason.
Obviously the first sage was powerful, and created the Ninja world, but failed to bring peace, right?
So they need someone to be greater than the Original Sage, or as great. Thus creating Naruto from all the histories Turmoil.
Through out the Manga their is little hints about Naruto, like Jirayia's Book, Because Naruto Inherited the will too!
I hope I made my point across, I know it's going to be broken a part by many, especially I Know I have horrible Grammar, and sentence structures etc.
But this is just an Idea. We wont know until the Manga is finished.
However, if my Idea actually become true, I gave the people reading this heads up.
Thanks, Guys.
I love reading everyones Ideas.
Oh btw, I think that Sasuke shouldn't get Rinnegan, or actually maybe that is how Naruto obtains them, maybe Sasuke gives Naruto his eyes.
I am just stating that, because all these motifs of Eye giving, right? Just an idea. I think Something tragically has to happen in order for Naruto to Awaken more things to become the sage, but that is why he can revive all those who sacrificed so much for Naruto.