To name a few accomplishments..
* If wikipedia is correct, he was the "48th most cited psychologist as of 2002".
* He has an extremely popular metric named after him (Cronbach's alpha)
* President of American Psychological Association.
Maybe what he is missing to the author is the popular media appeal Feynman has. However, I'm not sure that's a good criterion for genius, since I'm not sure it's something Cronbach wanted.