Even US Open - he has 1 slam. So does Murray. So does Nadal. So does Del Potro. Sure he's made more finals than them but he's hardly shown he's unbeatable there. Even if he's given US Open he's not a favourite at RG or Wimbledon. The top challenger after Nadal? Yes. Favourite? No.
In USO he will always be biggest fav with Olderer, they are best HCs in the world. Nadal...just no, and Mugray well, lets see how he will defend it. At RG Nadal cannot constantly win titles till he is 40, and after him Novak has biggest shot.