I can certainly see the solid case for Frazier here. Faster ,bigger,better defence,tougher skin . However I pick Marciano on the basis of his two handed power ,but I would not be betting a cent on the outcome!
Without making a list, I can see Marciano losing to a lot of men. Even ones who weren’t ATG’s. But to be clear, that doesn’t change my top 10 rating of him. What matters is that he beat the best of his own era, weak or not. And he established a record which more than half a century later has yet to be broken at heavyweight. People often wrongly label his record as being “ padded.” This is a fallacy… a padded record is only achieved when someone purposely hand picks opponents while steering clear of the threats. Marciano beat the best available fighters of his time and you can’t label an entire era as being padded.
Even if you made the strongest assumption against him based on his size, you might still expect him to do well against those who came before him.
The guy was the size you needed to be to be champion in those days. just like the guys now need to be the size they are in order to be a champion now. The size a heavyweight is now wouldn’t be possible in earlier eras. They would need to be smaller in order to compete then.
After looking at wikipedia's list of heavyweight champions there's at least 25 or 26 I'd favor over Rocky : Jeffries Johnson Willard Dempsey Tunney Louis Baer Charles. prime Walcott, prime Liston Ali Frazier Foreman Holmes Tyson Tucker Buster Douglas Lennox Lewis Bowe Vitali Wlad Wilder Briggs Fury Joshua Usyk some other's I'm 50/50 Holyfield, Norton, Witherspoon. Rocky could beat some no doubt, maybe Baer, Tunney, Walcott but he could also get beat up by some other's not mentioned. Just my opinion, I agree with Emanuel Steward , Rocky was to small . to slow . and lacked any reach whatsoever.
I could certainly see him beating the likes of Dempsey, Pete Rademacher, some of the old timers like John L, and Corbett...I think he struggles mightily against Quarry, that fight is a toss up, and I believe he proves too brutal for Usyk. As for the guys that beat him, I have Pattreson, Liston , Jack Johnson, Norton, Tysin, Holmes, Lewis, ibeabuchi, Chris Byrd all beating him. And holyfield too. I think young joe Louis and Frazier are both toss ups
Tucker lost to Tyson just like Mitch Green did. It was not a close fight. losing to Tyson is not a win. Tucker never beat anyone that good. Tucker lost to Orlin Norris both times so far as most people are concerned. And Norris had the same reach as Marciano.
I think he actually beats Johnson. Too much pressure, would win lots of rounds on sheer aggression. Bad style matchup. Against prime Louis, possibly 60:40 in Louis favor. He beats Tunney. Cuts off the ring and wears him down with body shots then stops him late. Tunney can't hurt him and wouldn't be able to outwork him enough to get the nod even if it went the distance. Jefferies might beat him just by outlasting him with his insane durability and keeping Rocky honest with his own respectable power and pressure. I think when two guys clash with offense oriented styles and a few similar approaches, the larger man usually wins. I generally agree that Rocky beats almost anyone under 200 fairly convincingly except perhaps Dempsey and prime Louis. Can't see him losing too many fights pre Liston era.