Drysdale, PMAC, and Cahill were all mediocre players. They won a total of 8 tournaments combined
Cliff was definitely not a mediocre player. He won a doubles title at the USO, made the finals of the Open in singles and was a top player in the 60's and 70's. He had quite a good career, actually.
P-Mac and Cahill were both mediocre, I agree, but don't discredit what Cliff accomplished as a player.