I think guys like Norton, Witherspoon, Cooney, Mercer etc are a lot closer in quality (not that much more stylistically similar, though) to Liston than anyone Dempsey beat. By the way, Evangelista would be the best Holmes had beaten if he had made the same distinctions concerning opponents that Dempsey did (only whites, except the best one of them). I know that's not a perfect comparison, but it does give us some perspective.
Hard to say given what we have to go on. In the footage we have Dempsey either easily outboxes big but limited fighters or outslugs small technical boxers. Tommy Gibbons who was a superior technician claimed that Dempsey was a good boxer: "Don't let anybody tell you that Jack Dempsey can't box" Gibbons could probably be compared to sombody like Eddie Machen and it apears that Dempsey has some success in outboxing him. Of course the acid test would be if you reduce Dempsey's power to the level of Gibbons and then see what happens. It is hard to be certain whether Dempsey could outbox Liston who had verry good fundamentals but he would have held an edge in both hand speed and speed of head movment so at the verry least he would have been a constant threat to catch Liston with a nasty countercombo.
How did Willard prove he had an "all time chin"? Willard was totally open against Dempsey, with a very limited arsenal. Patterson would land at him at will, and even though he wasn't at Dempsey's level as a puncher, he packed a nice wallop. I don't see Willard landing too much on him, either. Under the ruleset of 1919 it would turn out very bloody indeed for Willard. And Patterson's questionable chin stood up for everyone except Liston and Ingo. Dempsey's stood up for everyone except Flynn. I respect your knowledge Janitor, but I actually thinks it's you who is naive here. How in earth would Willard stand up to Patterson's speed and skill? The Archie Moore of 1956 was far superior to the Willard of 1919, but...
So if a LHW today swore to the solidity of the chin of a HW he had fought we would put what value in that? Ruiz must have been a monster, taking Jones' best shots like that.
Maybe because.... white people played sports more back then? Lots have changed in sports. In some sports there is significant prejudice against white athletes, like in basketball and the skills positions in football. As Janitor already pointed out, the ghettoes were chock full of whites back then, which resulted in a greater number of white athletes with the necessary temperament. This isn't very hard to understand.