Marcianos defense is a little underrated actually. He's short as a heavyweight, fought in a crouch, ducking real low, very awkward to hit when he wasn't throwing bombs, then rise up with a rabbit punch to the back of the head.
That depleted shell of a great light heavy that Marciano fought? The guy who wouldn't go .500 for the remainder of his career. Sure, plenty of guys.
Imagine if this were Tua instead of Walcott hitting Marciano at will... (and please spare me the part about how take a man of Walcott's all-world skills and canny to bully and hurt Marciano like this in the first round) https://streamable.com/m8wj
Marciano would beat the s**t out of this bum. Tua was a talentless boxer with good power and that wasn't enough against elite fighters as was shown when he fought them let alone ATG's.