Well his clay records speak for themselves. No one is breaking them.. At least any time soon. But there were guys comparable to Nadal on clay. Guys like Guga, Rosewall or Borg and perhaps a few others which could hold their own vs. Nadal.
And this era hasn't exactly produced NEAR the talent on clay that some past eras did.
Nole and Roger are probably the two other best clay courters of the 00's-present.
Taking nothing away from those guys.. They are good clay court players. But not GREAT