Easy, it's a long way... He started with a bang certainly, and right know he looks like successor of Merckx/Hinault, bit didn't Maertens and Lemond for example looked like that too? In 2013 we all thought that Quintana and Sagan would win bunch of GT's and Monuments, but they won 2 each (Ok, Sagan won Worlds 3x, but still...).I'm pretty sure Pogacar has already surpassed most in front of him, including Valverde.
I would say that the likes of Boonen, Cancellara, Contador, Valverde, Nibali, Froome are still ahead of Pogacar.