They're greater than albert costa....thomas johanson...petra korda....... I could go on....... The only one slam wonder they probably arent considered greater than is Andy Roddick, but Roddick made four other slam finals and had he not existed during Federer era probably would have won more. (that said they should be considered greater than him)A person with one singles slam is greater than a person with 100+ doubles slams.
For example: The Bryan brothers in ATP, none of them is greater than any of the slam winners in Singles.
Anyway, I dont think you can compare the two. Different games. Those saying when talking singles you dont care about doubles. I disagree completely. Look at the players who are tied in singles, but also played doubles....
Nav pretty much dominates Evert
Venus tops Henin
Hingis Better than Sharapova