I respectfully disagree.
Rocky would have k.o.'d him within 5 or 6 rounds.
I would also claim that Rocky ruled at a time when there was a dearth of great heavyweights, as did Floyd. However, his competition was still better. Bert Sugar rates Ezzard Charles amongst the top 5 heavyweights of all time. Rocky beat an aged Louis, who, imo would have knocked out Floyd even at that advanced age.
Floyd could hit, but his chin was fragile. The sad thing is that he never beat a great fighter, beyond Archie Moore, who was even older than when he fought Rocky.
I would even go back as far as maybe Max Schmeling, or Jack Sharkey or Primo to find a prior champion Floyd would be able to defeat. I think Max Baer would have knocked him out; Louis certainly; Walcott, Charles, Rocky, etc.
Floyd was a great man; but he was a mediocre heavyweight champion.