Even if he was mentally stable when he declared his revolution, his mindset was still cloudy for more than 600 chapters. I'm not saying he was mentally unstable, but he was in a great turmoil because of his extreme emotions. Before fighting Itachi, he was driven by his hatred towards his brother. After fighting Itachi and before hearing the truth from Obito, he may have found a momentary peace, but that was of course changed. Then he was driven by his hatred towards the village to the point that he would attack anyone without thinking clearly. That includes his former teammates, who he still cared for deep inside. Anyway, the point I'm trying to make is that Sasuke was constantly changing his mind, without being able to see the world in it's actual state (that's why he went on a road to redemption). On the other hand, Naruto was always sure of his actions, minus one or two moments where he was REALLY unsure. Naruto won by TNJ, but that win was philosophical, not physical as a lot of people say. He made Sasuke change his opinions and that was what made Sasuke lose, and Naruto win. Besides that, physically they are equals. Even if Naruto didn't want to kill Sasuke, he was pushed to his limits. When their jutsu clashed for a final time, both of them were offensive and that's enough proof that no one is stronger.