He is, he has 20 slams to Novak's 19 (potentially), and he has a olympic gold. Plus the point no one mentions, Nadal has been injured the most of the 3 of them, and still is tied in slams, masters etc. Imagine if he wasn't hurt so much and missed so many tournaments? But I'm saying, people will remember Djokovic as the GOAT, the only achievement he has left is overtaking them in slams, which at this point is almost a given