People underestimate how Federer wins his matches nowadays, so it is natural that people put him in the same category as Nadal and Djokovic, as a benefactor from a "weak era".
Nadal and to a certain extent Djokovic still compete on both physical and skill level, while Federer doesn't have that luxury.
They are besting their opponents in their own game, while Federer has to face the athleticism and the reflexes of the younger players with skill and tactics.
Nadal bulldozed his way to the RG titles.
Federer finessed his to the Wimbledon and AO ones.
It is a testament to Federer's ability that he could beat the players that he beat, missing major advantages against younger opponents, and especially against other ATGs.