smalahove
Hall of Fame
I don't understand the simplistic assumption that, to be a top doubles player you must be a top singles player. Doubles is a different game and requires a different skill set than singles. Heavy topspin drives which are the go-to shot with most singles players are less effective in doubles and, often enough, are the wrong shot to use. A shallow, dipping topspin drive might be a good tactic against a doubles player attempting to rush the net but it is not the right shot for a player at the net because it is is easier to effectively volley than a flat drive. While the top singles players like Djokovic and Nadal are solid volleyers, they are less comfortable taking the net than is required for doubles. In spite of the statistic that a singles player at the net wins about 2/3rds of the points there, top singles players prefer to stay at the baseline when they could safely take the net.
The #1 singles player, Djokovic, has one demonstrable weakness: his overhead. No top doubles play could afford such a weakness. A top doubles player MUST have a great half-volley. This shot is much less important for a singles play, particularly if he can just take the ball on the rise. But mostly, a great doubles player must develop an instinctive ability to adjust his court position in relation to where his partner is and where the likely incoming ball will be. Court positioning is simpler in singles because you don't have that partner coordination issue even though you don't have to cover as much territory as in singles.
Certainly being a top singles player in no way disqualifies someone from achieving similar success in doubles. The financial and status rewards are greater in singles so that's where the players go who can cut it in that version of the sport.
In addition, the best doubles team often have players with complementing skill sets, such as leftie/rightie, great returner/great close combat net, aso. And compared to a team comprising of mainly singles players, the best doubles teams work together as a team, at a much, much higher level. This can be seen as: much more dynamic movement around the service line and at net (singles players most often stand pretty still), much more coordinated movement (they move together around the net, change places aso, at a very high speed) whereas singles players often move slow. Thirdly, their actual tactics are much more refined. Singles players often resort to hammering balls or perhaps singles play type of shots.