Prime for prime who wins this fight? Both were the KO artists in the HW Division who could knock out their opponents by a single punch.
Different eras. If Tyson was born in 1929 and came up during that time with the limited knowledge on training methods, sports medicine and even fighting in general... then Rocky all day. Marciano had a non stop mindset even when the going got tough. Tyson... you could knock the fight out of him as we saw.
If Marciano made it go the distance then he would have a chance to beat Tyson. But I think that Marciano could not survive the first 5 rounds.
I like your thinking on this, but that's not how comparing boxers from different eras works. Everytime RJJ or Holy would be put in with a current fighter, they mean the juiced up to the brim versions, that wouldn't even pass a simple USADA test nowadays. So the negatives or positives from the era are not taken into account.
Marciano wasn't a heavyweight. He was barely even a cruiserweight. Why do people persist in making mismatches like this?
Basically what the others have said: they were both sluggers except for that one was about 30lb bigger. Tyson has to be heavily favoured here. Nevertheless I'll try make an argument for Marciano. Rocky wasn't nearly as easy to hit as he's made out to be. By the time the second La Starza fight rolled around he had developed some real skill. Moreover, he had the winner's mindset and would not be intimidated by Tyson. This is a man that would truly rather die in the ring than quit. Rocky's best chance lies in his punching power, which was in itself shattering, and his stamina which was unsurpassed. He'd have to land something big early on to get Tyson's respect, and he'd have to keep the fight really close and mauling to minimise the disadvantages of his t-rex arms. If Marciano made it out of the first 5-6 rounds more or less intact then his chances go up exponentially. In fact, if Marciano made it to round 6 in one piece, I would favour him from then on out. This is a man that could truly fight as hard late as in the first, whereas Tyson's effectiveness dropped markedly in the later rounds. The real question is whether he'd make it to the late rounds, and I think probably not in good enough condition to carry the day.
Rocky was about the same size and weight as a rehydrated Artur Beterbiev. Dempsey was about the same weight and dimensions as Sergei Kovalev. Both these guys are beasts, but how would you realistically expect them to do at heavyweight, let alone against one of the most fearsome heavyweights of all time? Just think people need to get a bit more perspective here.
I don't think that it's a mismatch. There were bigger opponents in the HWD who got KOed by Marciano. He knew how to beat them. I know that during his era Marciano never met a formidable opponent who hit as hard as Mike Tyson and I think that Tyson would KO Marciano if they both met.