Re: Has Djokovic surpassed Stefan Edberg and/or Boris Becker?
No significant difference in surface does not equate easier to dominate slams. There will be more good players to adopt their games to be better on the surface. Sampras had a hard time winning on clay because his game, which was perfect for Wimbledon, has many holes for RG. He tried to adjust his games to better on clay but it affected him on glass. Vice versa for clay specialists who did not even bother to show up in Wimbledon. You have a set of players who were great on Wimbledon, another set on Roland Garros. Even for the faster hard court for USO and the slower for AO, there are more overlap of players but still, some stand out more.
Now on the medium pace hard courts, all the top 4 players are actually very good on it. Even the rest of the top 10 can play very well. Thus, it's not that easy to dominate.
How many players in modern era managed to win all slams? And how many managed to win all slams more than once?