Every sport demonstrate that. In the beginning of every sport, we had massive differences between riders/teams/clubs and the tendency is to this gap reduce with time.
We no longer see a player so dominant as Hendry or Steve Davis in snooker (or Joe Davis in the beginning of the sport)
We no longer see Real Madrid or big national teams win 10-0 regularly.
We no longer see a franchise like Celtics win and obliterate the NBA.
We no longer see a rider like Merckx in cycling that win every important race.
I have nothing against Merckx however we have a different sport now, a lot more competitive and balanced sport with way more professional riders.
For me Pogacar is the GOAT of "new cycling" (specialization era).
Yet we see the likes of Hamilton and Verstappen obliterating F1
And we see Man City on it's way to win 4 PL titles in a row (not sure if it's been done ever..)
And we see Juventus and Bayern winning 11 or something in a row.
Not to mention that we see the like of Shifrin and JTB and Hirscher and so on in the winter sports.
And we see the big 3 in Tennis dominating ATP for nearly 2 decades, destroying most of the records.
And yes, O'Sullivan is more successful the Hendry and Davis only that over longer period.
To put it like that, nowadays we have as many people/teams dominating sports, as we've had before. It's far from certain that Merckx wouldn't win as much or even more nowadays.