For me, 24-25 y.o. Federer was better than Nadal, Djokovic and Murray.
But for many people is just the opposite. You now, how they say, "the game is always improving".
Even Agassi thinks Djokovic's and Nadal's peak levels (and Murray's peak level too) are higher than Federer's peak level.
And the nš1 player in 2016 would defeat 6-0 6-0 6-0 peak Federer (or peak Nadal or peak Djokovic).
This is what they want to sell and many people agree with them (amazing).