There is doubting his quality but i don't see him as the greatest tennis player of all time nevermind greatest sportsman. To be the greatest tennis player you have to excel on all surfaces. As we have seen Federer does not do so well on Clay.
He can beat abyone if he puts his mind to it. No ,atter what type of surface he's on. He did beat Nadal on clay court. I thinhk he's one of the best tennis players in all time history along with sampras and agassi