I'm not sure how Clapton could be put in the category of "overrated." He succeed with groups - Yardbirds and Creem, one-offs like Derek and the Dominoes, and on his own.
How many other artists, American or British, have done that in rock? Robert Plant, perhaps, for a little bit. Rod Stewart. Certainly, Phil Collins. I can't really think of an American musicians who did well for decades after being successful with a group.
And, has any guitarist been as successful for as long as Clapton? I can't think of a guitarist who has outsold Clapton on either continent.