Did they changed GS surfaces recently? They are just not that good on main tennis surface where the competition is the highest. When they started playing tennis it was the same surface distribution of slams as it is now. USO changed to HC in 1978 and AO in 1988. Champions learn how to be the best on most represented surface in sport. Why they where not able to be the better on HC knowing this? Did someone prevented them to practice on HC from their childhood? Why do you think some players specialise in doubles and not singles? You really think that level of competition for last two decades is the same on clay and grass as it is on HC? Its actually the opposite of what you wrote.Djokovic is way down pecking order. How many Majors would Nadal and Federer have if they had two on their best surface?