I agree with that post (that there have been countless anonymous special talents...and that large concentrations of Einsteins may be impossible), but I think it's a separate point. My main point was that although great intelligence drives knowledge revolutions, when the knowledge is passed to others, the intelligence that created isn't transferred too.
I.E.: Humanity keeps inheriting better books to read with the same class of brain.
Also: "Genius" is probably an overused (or at least poorly defined) term. He'd probably have been fine with it, but I think stopping at genius is an insult to a guy like Boltzmann, Darwin, or Feynman. In that school, the threshold for Mensa is kindergarten at best.