I never said he was, did i? At any rate you're downplaying Marciano but it's a schtick I'm well aware of as well as immune to.
Marciano wasn't a great heavyweight by 80's standards. Dude would have been great on the Senior Cruiserweight Tour.
A lot of Marciano opponents were not far over the light heavyweight limit themselves so power wise I would guess they were probably similar to Spinks light heavyweight opponents. Certainly they were likely far closer to them power wise than the likes of Tyson or Ruddock (big hitters by 80s standards). Moore continued fighting at light heavyweight years after fighting Marciano. Spinks fought 5 guys over 175 prior to moving up for a total of 9 heavyweight/cruiserweight opponents. Holmes, Berbick, and Thomas were all renowned for their durability and Berbick was never stopped subsequently despite fighting into his 40s and facing Rahman, Douglas, and Williams. I thought we were using the bulked up heavyweight version for this fight as that was the better version H2H. Regardless the light heavyweight version was far more consistent than Marciano's opposition. He wasn't losing a third of his fights like Wacott and wasn't past prime like Charles, Walcott, Louis etc. Do you really see Spinks even the light heavyweight version losing to the guys Walcott lost to or the guys Charles was losing to at that stage of his career?
Marciano can do this. Some of the better bigger heavies might be out of his reach but he has the durability to walk through Spinks best punches and land his own. Over 15 I’d pick the Rock
Marciano by late stoppage. Many would make Rocky look bad, for a little while anyway, but in the end I think he would catch up to Spinks and stop him.
Prime Spinks is not an an over the hill older fighter. He will not run out of gas. Also Rocky is going to have a hard time landing a solid shot on him and he will land some punches that Rock wont even see. Ask Cooney and Holmes. The beating will accumulate with little damage sustained by Mike. No one can survive that indefinitely.