Whether or not Thomas was affirmative action in the eyes of 41, he is certainly one of the best justices in several generations—I can only think of two, Alito and Scalia, who I would place in the same category as far back as my mind can evaluate in a reasonable way.
Justice Thomas replaced Thurgood Marshall. No way anyone but a black man was going to be selected for that vacancy. So one could say that Justice Thomas is proof positive that even an affirmative action appointee can turn out to be an outstanding selection.