What makes so many people think Nadal does so well? He's gonna be kinda rusty given he didn't play for 6 months....
it's especially Djokofans if you look carefully : they are afraid that people may be too confident for Djokovic next year then they try to wonder if there's not something they might worry about which people may have left somewhere, and the problem is that they don't seem to be able to be afraid of Murray (they're wrong for that imo) and they (rightly) think Fed is too old,
then who's the threat they think they can reasonably fear ? the big absent, Nadal of course !
he's for sure a great player but not only he comes from 6 months injuries, he also starts having many many years on tour for a player with such a style and history : from his age this year, Borg, Wilander ... and McEnroe (all having similarities with Nadal in their own way) didn't take part in any slam final anymore. Edberg reached his very last slam final precisely at 27 years old, the age Nadal will be in Roland-Garros.
And Djokovic has proven that he knows how to play against him very well now. Even when he lost on clay this year, it was a very disappointing Djokovic who did that. His match-up against Murray he's still ahead but it's more worrying imo.