They would do the same , you gotta pay attention to how rocky fought, he didnt just walk forward upright and get abused . He would wait for you to jab first then parry that jab and or counter and get inside and rough you up. I did analysis of his fight with Joe louis and joe landed his jab against rocky 15.8 percent of the time and ate more counter punches (20) than jabs landed (16) against rocky. Jess was a fine jabbing big man but that would work against him here.
I'm not disputing LaStarza. He was pretty decent boxer. I don't really know if we can be that certain of Dempsey's talent. He had some ability yes. He didn't test it to the extent he needed to. How would he have solved a Harry Wills? A man who was both big and quick. Dempsey squandered the talent he did have.
You could certainly make the case for Marciano being greater than Dempsey, but Dempsey was the better finisher of the two, and the better at overcoming a size disparity. These are critical traits when you are a sub 190lb man fighting somebody like Willard.
It boils downs to tactics and strong traits for me , Jess would beat someone who couldnt get past the jab (braddock) but Rocky built his style off you jabbing , I dont know if he hits Willard with those overhand counters(reach difference) but he certainly can parry and get inside and thats where WIllard will drown. Ultimately Marciano stops Jess Willard!
You would be justifies in making Marciano favorite, but Willard had a dangerous uppercut, indeed he killed a man with it. He would also use his weight to lean on Marciano, and hope to tire him out in a longer fight. Of course that would result in him taking some nasty shots to the floating ribs. His jab is not his only tool in this game.
I don't think he'd do as well as Marciano. Rocky broke guys down over the course of a fight, whereas Dempsey tried to blast them out really early. Dempsey did well against big guys because he was so explosive and hard hitting. I don't fancy Dempsey nearly as much against Charles, Moore, Walcott and heck, even LaStarza as I do Marciano. I suspect that the good boxer types would have weathered the storm and had a good chance late. Whereas Rocky simply plugged away harder and harder and smashed them to bits. Dempsey would win his wins better, but I think he'd also have losses.
Dempsey lost four times inside the 49-fight limit to fellows most fans here don´t even know of. So the answer is obv. no.