This is different from "Worst Actor," but the responses are already strange.
James Dean? Don't think so. He would still make it in the movies today. Not many screen actors today have also been on the Broadway stage. It's the untimely death that makes him a legend, an actor that still has a website devoted to him:
Ronald Reagan was never over-rated but overworked. Not sure other than his looks why he got some of his roles but the movies were nearly all B movies and not that many were starring roles. He was shoveled into television earlier than almost any actor I can think of, never was nominated for any significant film award, and his star on the Hollywood Walk of Fame was for his television career (and, obviously, his ascension in politics). He wasn't even a good actor as President. Unless you like moribund with some home-spun hokey Reader's Digest humor.