Yes, I think that the amateur ranks were severely depleted in the late 1950's, with the top 8 players all pro, plus other good players such as Rose, Hartwig, McGregor, Giammalva, these 4 also major winners (Hartwig a runnerup at Forest Hills in singles). The amateurs only had Olmedo (who signed to the pros in 1959), Fraser, and Pietrangeli in mature form. There was more height and depth at the pro level. Not so in the mid-1960's. In addition to Emerson and Santana, who apparently made more money than the top pros, there was McKinley, Stolle (until 1967), Osuna, Ralston (until 1967), Newcombe, Roche, Ashe (a star from 1965 on), Fletcher, Krishnan, Bungert, etc., while the pros could only boast, in addition to Laver and Rosewall, players who had never won a major, (Bucholz, Gimeno) plus ageing Hoad, Gonzales (after 1964), and a disappointing Olmedo. More depth in the amateurs.