Not to diminish his greatness, but could he have defeated Joe Louis or Rocky Marciano at their prime?
Don't know about Joe Louis,but Rocky knocked his ass out when they were filming that boxing video game,and Rocky was a old man long-retired at the time.
According to the producer,he hired them both to do a fake boxing match where no actual hard punches were thrown so he could record their moves to make the video game realistic,but Rocky warned Ali twice about throwing hard punches to the face,and the third time he did it,Rocky put him on his ass. Once Ali could stand again and remember his name,there were no more hard punches thrown at Rocky for the remainder of the recording.
What got Cassius Clay so pissed at America to start with is after winning the Oympics boxing Gold Medal,he came back home and bought new Harley's for him and his brother. The first time they took off riding them,some white guys beat them up and stole their Harley's.
What Clay was in the ring and out of the ring was be a VERY smart boxer and he could take an amazing amount of punishment. Make no mistake about it,he was genuinely tough. Any damn fool can throw punches,but you have to be seriously and genuinely tough to take some of the punches he took and still be able to fight back.
IMHO,he wasn't really all that good,though. What he did was run his mouth and really,REALLY piss off his opponent to the point the opponent would lose his cool and throw his strategy out the window. Then he could wear out his opponent by letting him throw punches that mostly hit his arms,and when the guy was too tired to really defend himself,he would then step in and start hammering him. He mostly beat his opponents by out-thinking them and getting them psyched out before the fight even started. Better to fight smart than it is to fight hard.
He never agreed to fight anyone he thought could beat him,and even then Ernie Shavers beat him so badly in the match that Clay finally gave him when he was really too old to fight at that level that even I was feeling sorry for him. I remember thinking "DAMN! It should be illegal to hit ANYBODY that hard,even Clay!" If you have never seen that fight,try to find a video of it. I didn't even know it was possible to hit that hard. It's a little scary to even watch it. Ernie Shavers was an animal,and after watching that fight you will know why all the top boxers avoided giving him matches when he was younger. You can't get a title if no one will give you a title match.