Most of the people back then could do everything Roger de Vlaeminck could top 10 in GTs.Merckx is the most complete and talented rider ever.
He was also a sprinter who could beat those guys in a flat stage.
Nowadays you have MVDP dominating classics but nowhere to be seen in GTs and Vingegaard dominating GTs without bothering about pne day races.
That's why Pogacar is so special. Because in these years of specialization he's doing what Merckx was doing back then.
Fairly sure Merckx wouldn't win half as much nowadays
Fairly sure Pogacar would win more if Vingegaard wasn't all about stage racing