Well, based on his total amount of majors your argument is a good one IMO. 7 out of 8 French titles is hard to surpass in any era.
But as Sumarokov-Elston points out, there are some factors in his dominance. Just as Chris only had Evonne, who does Nadal have as a rival on clay? To me it's a sort of chicken vs egg argument.
Nadal has had Federer and Djokovic for years as rivals on clay. Federer most regard a top 10 clay courter all time, some would say top 6. Djokovic will likely become a top 10 or better clay courter all time by careers end, and he has been an excellent clay courter since 2008 atleast now, continously held back by Nadal mostly (Federer to some degree). That is head and shoulders above anything Chris had until 1982 atleast. Even after that you had solid performers like Coria (until 2006), Ferrero, Davydenko, Nalbandian. Who was Chris's biggest rival on clay in the mid to late 70s after Goolagong. Virginia Ruzica? 35 year old semi retired Nancy Richey. No offense but what a joke.
Does Rafa's (or Chris's) great record rest on their amazing abilities, or on circumstances favorable to them?
Both would be great clay courters in any era. However Rafa did have tough competition on clay always. Chris had no competition on clay from 1974 to 1981.
Frankly I don't see Nadal winning all those French titles vs Borg, for example. Bjorn would simply loop back enough balls (as would Rafa) until one or the other dropped dead. And unlike Chris, he has lost on clay outside the French where conditions vary and it's 2 out of 3 sets vs 3 of 5.
Borg and Nadal are the two best clay courters ever so they would have to be insanely unlucky to have ever been born in close to the same year. Nadal's clay competition is fine, it is as tough as most people had, and tougher than what Borg had. The 1974-1979 clay court field for women (possibly for men too come to think of it) is bar none the worst in tennis history, including even the post Henin years on clay year. Just look at the French Open winners from 1976-1978, and I dont care if a few people didnt play.
And lets be just as honest-Chris would be hard pressed to be unbeaten for 125 consecutive matches on clay vs the likes of Seles, Graf, or Henin under "modern" post-wood conditions.
Without a doubt. Meanwhile Nadal would have duplicated most of his current stats in any era. Only if you put him in the era of peak Borg or peak Rosewall might he have suffered even a bit from his current record, but they would likely have suffered even more, since he is even better than they are. Chris meanwhile would have not even approached her current stats on clay peaking in the era with Court, Richey, Jones, all as clay competition, or with prime Navratilova and even prime Mandlikova and young Austin as competition on clay, basically any era except 1974-1979, that is probably the only time in history she could manage something like 6 years unbeaten on clay, even as great as she was on the surface. Certainly least of all in the era of Graf, Seles, Sanchez Vicario, Sabatini, and others which was the deepest and strongest clay court field ever, and why I think you could even make an argument Graf is the greatest women clay courter despite winning only 6 French Opens and the Seles stabbing, or perhaps Seles herself, but that is another topic. Either way Nadal >>>>> any man or women in history on clay.