Jack instead of Deontay would make a world of difference I think. AJ beats Dempsey Jack beats Fury Tyson beats Joshua
So AJ wins because he's bigger and newer? Great stuff. Dempsey was far more experienced plus, more importantly, he's a bad styles match. Guy who doesn't move his head, is nowhere near as tough as Willard, and stiffens up when buzzed against Dempsey circa 1918-21... AJ could hurt Jack. Dempsey would acknowledge the risk, pick his moments, and find the angles.
Anthony Joshua was better than Jess Willard and he would probably last longer than the 3rd round, but not much longer. I am going with a win for Jack Dempsey, by stoppage, between the 4th and 6th rounds.
I can definitely see your point. I was referring to the fact that Dempsey retired immediately after while Holmes went on to be a force in the division and arguably should've picked up a belt. And while you're correct that Holmes would likely have not beaten the number 2 HW by that point (out of curiosity who was it, Spinks?) I also doubt that version of Dempsey would've beaten the number 2 heavyweight of Tyson's era as well. Though perhaps who was more declined could be answered differently depending on how good they were relative to each other's eras, as well as their own.
Dempsey retired immediately after the second Tunney fight never to return, but he beat the worlds #2 HW beaten Tunney 1 and 2. Thinking about it properly, given you've asked, I suppose technically Tyson was the #2 ranked HW when he beat Holmes, given Spinks was the lineal champion. Clearly Tyson was the best HW, though. I suspect other HWs at that time, including but not limited to, Spinks, would have beaten the Holmes that Tyson beat. Yeah, no argument from me there, though I don't take fantasy fights from vastly different eras seriously. Different conditions, different times, and in this case, even different sports/rules. The Dempsey that lost to Tunney was clearly past his best, but he was both better for his era than the Holmes that Tyson beat was for his, and was the closer of the two to their respective primes (as you'd expert a 31/32 year old to be relative to a 38 year old).