Well Pogi is about as close to winning bunch sprints on the Champs Elysees as Wout is to winning a GT...not close but also not unthinkable. But if you want to say Pogačar is the best bike racer in the world you have a great case. I just don't see him as nearly as versatile as Wout. Wout wins in disciplines where it just doesn't cross over. Guys who win field sprints do not win TT's and mountain stages in GT's. Except Wout. That's where he's more versatile. GT winners have historically won big classics, that's not unheard of. What Wout is doing hasn't been done since Merckx.
I have a hard time getting my head around that statement. It seems objectively wrong unless you basically ignore everything in cycling except winning the Tour. A Tour win is worth more than anything in cycling, no question. But that's basically all he has, a win and a second. Good Dauphine results. He's a great stage racer now. Most of the season he's invisible.
In the evaluation quadrant of prospect/retrospect and results/ability, it's still the case that he is far from the best in the world in one of them (results, namely big wins, so far). A similar (but lesser) case is that of Sagan after the 2015 Tour. Was he at that point among the best 3 riders in the world? If so, he didn't have that much to show for it.
As for possible great wins of the future, I think it's a valid point that Van Aert's climbing ability will mostly pay out in classics, one-week stage races and single stages in GTs (and the polka dot jersey as well), like Ventoux last year. How much are great GT stage wins worth on his final palmarès is a matter of taste and depends on what else is there. I mean, would a stage win like that over Ventoux add much to the palmarès of Kelly?
Since Merckx? I'd say you 'only' have to go back to Hinault, as he did win the sprint in Paris.