You just said it yourself, that Nadal will prove it on clay against Djokovic. But thats not a proof to me, a proof would be a victory of Nadal against Djokovic on another surface. Or a Grandslam title of Nadal at the other 3 Grandslams besides Roland Garros.
Nadal is a great player for sure and he improves on other surfaces but he wont be as strong as on clay. Look, he was training his whole life on clay while others like Federer and Djokovic had to play other surfaces, of course they cant adjust as well as Nadal on this surface.
And about behaviour on court. Nadal is not the most sympathic on court either. Offcourt is a different story of course