He is a case where majors won is by no means a fair criteria to represent his power or dominance. He beat everybody for years even if he did not enter or win the the pro majors all the time. Arguably WW2 stalled his rise in the game but he was a demon on court. I am not sure where on a list he would fit though.
Top 15? Does he really merit a top 10 spot?
On the promotional side the man was a genius, he took the game to all kinds of new levels and venues. Billie Jean King probably learned a thing or two from him he was a dynamo.