Not even Ali believed that. He openly admitted that he didn't know how to beat Norton, but thanked the judges for scoring it for him anyway.
I think he has been rated accurately. A great fighter against boxers, but one who could not stand up to a puncher.
Past his prime he had one of the greatest heavyweight championship fights of all time against absolutely prime Holmes. I gave it to Norton by a point. Close but clear. Ken very was very unlucky. The best never to win the heavyweight title (the real proper heavyweight title anyway)!