Dempsey certainly brings a number of significant advatnages, but I think Marciano's measured approach would ultimately prevail
Marciano was too cute and would have traps ready and waiting for Dempsey. The Mannasa Mauler walks onto something big giving Rock a stoppage victory
I wish we could have seen a prime Kovalev vs Beterbiev. That would have gone a long way to answering this question.
The short answer is yes. Dempsey was faster off the starting blocks, and that might have been critical!
As admirable as marciano was as a fighter hes going out against dempsey.... He never saw the day he could ever beat dempsey... Dempsey was in another class
Despite my misgivings regarding Marciano's era, those guys were head and shoulders above the guys Dempsey chose to fight. We know more about Marciano's potential because he was battle tested against higher caliber fighters. We assume that Dempsey could beat better than he actually faced, in part because of the limited estimations of his contemporaries. But there are too many questions his career left unanswered.
I asked Bert Sugar this on one of the old ESPN Boxing chats they used to do. His answer was Dempsey in the first 4 rounds but every round after that his chances go out the window and it favors Marciano. I tend to agree. If it goes anything past the first several rounds Marciano wins. Would be one hell of a scrap that is for sure. Would be an exciting fight.