So Sampras and Agassi were in the same era as Fed? They were still playing each other 10 years ago???
I am just so sick of people trying their very best using stupid explanations to try to discredit Djokovic's achievements. Imagine Djokovic would go on and win 18 -20 Slams to better Fed's number and people will still use the same pathetic excuse, oh no his Slams were easier to win so they don't count bla bla bla
Look, Djokovic turned professional in 2003 (paying first tour-level event in 2004, making first major appearance in 2005), Federer in 1998. This means that for ALMOST A DECADE they have both played on the tour. They have faced each other 29 times in that period. They have had the same surfaces to contend with, the same racquet technology to benefit from, etc, etc. So yeah, they have for a SIGNIFICANT portion of their careers played together, won major tournaments, etc.
Meanwhile, Sampras retired in 2002 (turning professional back in 1988). Although their careers overlap, Federer and Sampras did not spend much time on tour together, so I think it's fair to state that Federer and Djokovic have shared an era in a sense that Sampras and Federer have not. Sampras played the majority of his tennis before Federer turned pro.
As for Agassi - his career extended into his mid-thirties, having turned pro back in 1986, he was still playing pro tennis in 2006(!!)
Anyway, I'm not trying to discredit Djokovic's majors, nor Federer's, nor anyone else's. But they have benefited from the fact that conditions across the majors are more similar now. Federer has admitted as much publicly.