I'm going with Dempsey. Baer's defense was terrible and a lot of his shots were wide looping telegraphed bombs that the faster more skilled jack could avoid and counter with ferocity. I think we're looking at about a 7th or 8th round TKO or KO..
Change it to Max Baer vs Luis Firpo, then Max could be fighting someone nearer his "skill" (for want of a better word) level.
Dempsey. They sparred a lot in tours they did in the period when Max was in his prime and Dempsey was old, and Dempsey was still better than him.
That probably tells in Baer's favor. In a time machine fight, Baer has extensive experience with Dempsey's style. Toledo Dempsey never sparred Baer.
Max Baer is such a strange fighter. There are times offensively he looks so technically sound and would come out with these bursts of speed for short periods. He was almost like a modern wrestler in the ring playing to the crowd . Him and Buddy (not enough film on Buddy!) were fun to watch. But Jack KOs him in 4. I could see him taking out some greats with weaker chins but he won’t last long again the serious power hitters. His defense looked on film nonexistent unless I’m watching it wrong lol.
