At least Orantes won a clay court major and in such an excellent way, beating Nastase, then mounting an incredible fight back against Vilas, then comprehensively outplaying Connors after an incredibly short turnaround time and hardly any rest.
But still seeing that he won 569 matches on clay, I think it's a big shame that he never won the title at RG. To me he's by far the best player, both in terms of raw ability (what a joy he was to watch when he was on-song, unleashing his magic and displaying his tremendous craft and touch), and credentials on the surface, not to strike gold there in the open era. He literally won everything else of note on the surface, including Rome, Hamburg x 2, Monte-Carlo, Barcelona x 3 and Madrid in Europe, and the US Open, Canadian Open, Indianapolis x 3 and Boston x 2 on har-tru.
He was favoured by many people to win the title in 1972 before he was upset by Patrick Proisy in the semis - he had won 16 matches in a row including the Italian Open and a 6-0 6-3 6-3 demolition of Proisy in the Davis Cup in the same Roland Garros stadium 2 weeks earlier. An all Spanish final between the 'old' Gimeno and the young Orantes would have been fascinating. 2 years later, he was of course 2 sets to love up against an 18 year old Borg in the final, before Borg fought back very strongly during the last 3 sets. In 1977 he suffered a lower back injury during his run to the final at Hamburg (where he also suffered a neck injury the following year vs. Vilas in his SF), playing through he pain barrier during his defeat to Bertolucci, but then had to withdraw from RG (when if healthy he could have been a serious title contender).
On the flip side Courier, only winning 115 matches on clay during his career per the ATP website (for players from earlier generations it's highly unlikely that the listed figures will be correct - for players that spent at least the bulk of their careers in the 90s onwards, they'll at least be more accurate), but back to back RG titles (including a very dominant title defence in 1992), nearly winning a third consecutive title there in 1993, a 4th consecutive semi-final appearance there in 1994, and back to back Italian Open titles, was incredible 'efficiency'.
I'd assume that the only other player that both played at least predominantly within the open era and won an open era clay court major (so excluding Rosewall, Laver and Gimeno although the first 2 at least definitely still won more open era clay court matches than Courier), with fewer wins on clay was Chang with 107. Apart from Chang, I'd assume that the only other player to reach a clay court major final in the open era, and record fewer wins on the surface, was Murray (109).