Anyone who gets KTFO in one by Fireman Jim Flynn, is NOT going to see round 4 against Lewis. At the risk of incurring McVey's wrath, the only round 4's that Dempsey would see would be in the undercard fights.
Dempsey like Johnson, like Louis and like Marciano and Ali were ALL ATG fighters with ATG abilities. To cut Dempsey short against anyone is a huge mistake. Jack was super quick, super determined, tremendous heart and will to win and carried a hammer in each fist. He would be a difficult opponent for anyone in any time period to beat.
I don't know why you think Dempsey is a top P4P HW, he had no jab, was left hook happy without much of a straight right, had a poor defense, was poor at long range and was often outboxed by the better quicker outboxers of the time. Tunney is obviously the better P4P fighter of the 2.
Smith in an interview the year before he died stated that "he hit Willard with a right hand that tore his ear clean off and he just kept on coming"
Overcoming weight disparity isn't the only or most important aspect of P4P lists, general quality of opponents is generally considered more important. But anyway I don't think that's true, Louis overcame similarly sized men weighing only slightly more, Spinks beat Holmes and ****ey, Holyfield overcame large weight disparity against suprior fighters, Haye overcame Valuev who was 100lbs heavier than him. Gunboat Smith and McMahon had already beat a younger more primed Willard weighing less than Dempsey. I'm not against HWs especially smaller HWs having high P4P rankings but I don't think Dempsey merits consideration based on resume. Again that's not the sole criteria for P4P status, Tunney beat better quality opponents than Dempsey did even if they weren't bigger
What better quality heavyweights did Tunney beat? Willard had about a 100 rounds of pro boxing under his belt when he fought Smith whilst Smith had engaged in 44 fights.
It's unfair to compare Dempsey to Lewis. Lewis would completely dominate dempsey with the jab, and then pulverize dempsey with the uppercuts on the inside and then push dempsey back off again like he's a rag doll. Dempsey is just too small for Lewis. Yes Dempsey has beaten huge guys before like Willard, but technically they were nothing compared to Lewis.
Dempsey and Greb, Greb having beat most of Dempsey's comp emphatically. I don't consider Dempsey as having a better win than either of those. Then there's Risko, Weinhart and Heeney who'd be considered top10 guys for some part of this period. Also there's the Carpentier and Gibbons wins.
Johansson Haye 190lb Holyfield Marciano Louis frazier Langford Fitzsimmons Schmeling patterson all knockout the 37 year 4 year inactive willard in under 7 rounds I think it's laughable to think a 185lb fighter being able to knock out a 37 year old 4 year inactive Willard in under 3 rounds instantly raises his stock to one of the best p4p of all time I'll take a 185lb fighter who can decision Harry wills and Harry Greb and place him much higher on the p4p list Quality is everything