100% spot on--GREAT post! (Exactly what I was going to say in my own words but you beat me to it LOL!!)
Top ten contender who started as a MW in amateurs and was LHW 175 pounder cant be compared with heavy like Weaver who held the title for 2 years and was a real HW. But he beat Berbick while Martin beat who except losing against Bonavena who was B level fighter? Didn't Snipes fought Greg Page and gave him helluva fight too?
Holmes in 40s beat Mercer and went 12 rounds with prime Hollyfield and McCall so no age excuse this time.
It seems like whenever Holmes gets put up against an opponent of Ali's, people forget that he has all of the same advantages that he did, and likely more in most of these match-ups. Holmes' style is simply an offensive based variation of Ali's style (which was defensively founded), combined with advanced framing and guard manipulation.
Holmes does not have the same advantages as Ali. Holmes isn't as quick as Ali. There is a considerable difference in footspeed and handspeed. Ali was also a far better and quicker combination puncher. Ali could do unorthodox things like throwing fast lead right hands.
I don't believe that the disparity in speed between Ali and Holmes would be significant enough to make a difference against Liston. Liston got played by guys like Machen, and he was in no way as fast as either of the previous men. Holmes was also less of a combination puncher mostly due to that difference in speed (Also likely because he had longer arms), so instead he'd simply hit the opponent with a few good punches. That difference in speed allowed Ali to slip illegal punches and chops and deal more damage.
I haven't seen the Liston-Machen fight but i remember Liston winning quite comfortably. I think it does matter. A fighter who is a 10/10 in speed (especially footspeed) will get hit less than a guy who is a 9/10. Even if Liston could land 10% more punches on Holmes than Ali in the earlier rounds, it would slow Holmes's legs even more and make him more vulnerable to bigger punches in mid rounds. That relatively small difference in speed can be quite substantial. I think the combination punching matters because it allows fighters to do more damage. Ali landed blistering 5-6 punch combos which buckled Liston. This made him more hesitant to come forward. Could Holmes hurt Liston the same way? I am not sure. Could Holmes decision Liston? Possibly. A stoppage is highly unlikely. Holmes had a habit of standing flat footed even in his prime. You can't stand flat footed in front of Liston.
We can't really use the Ali fight as evidence for anything because Liston not only came out to brawl, which was extremely uncommon in his prime and was one of the reasons that he lost much quicker, but also because he was past his best. What we see in the Ali fight is circumstantial, and that's why I keep circling back to the Machen fight, because Machen was the most like Ali and Holmes, he was simply smaller. I just went back to view some footage of both Ali and Holmes, and from what I see, the speed difference really doesn't seem apparent. I only see a difference in speed during combinations, mostly due to Holmes throwing straighter, longer punches to deal damage, whereas Ali would throw short, curved shots to pour it on. Go back and look at Holmes dancing and jabbing around Norton, that true prime Holmes was far too light on his feet to be called flat footed. The only time that Holmes would really plant down was to throw strong punches, and they worked, he definitely rocked Norton more than Ali ever did.
Have YOU seen this fight? Machen gave Liston issues and made it tough for him to land cleanly, alongside being one of only 11 fights that Sonny won when going the distance. And, I apologize in my wording again. From what I remember, there weren't any other notable movers that gave Liston issues in his prime, but I do believe that the issue would present itself again if Sonny faced any similar men at his peak. I think it's pretty easy to understand that Liston struggled because of how Machen fought, and not because of it being him specifically. You can compare it to Young - Foreman in that sense.
Bear in mind, too, that Ali was fighting top contenders almost exclusively for the last 40 of his 61 fights. A near 70% KO record is impressive enough where 2/3, not 1/3, of your fights were pre-title and your record's being padded with relatively soft touches. Ali scarcely had this luxury. He was up against top opposition from fight 20 onwards. There are few gimmes after he won the title in 64. His opposition in the warm up fights in 1970, and then his post FotC opposition. was sterling. Quarry, Bonavena, Mac Foster, Blue Lewis, Joe Bugner, Joe Frazier, Ken Norton, Jimmy Ellis, Patterson, Mathis and more I can't think of all comprised non-title opposition. That's crazy. It skews his kayo % record. Others take a less risky route and are lauded for their amazing kayo percentage (yes, George Foreman. I mean you). Not saying Foreman isn't a better kayo artist than Ali but maybe the gulf between them isn't as big as the difference in KO percentage would suggest.