I would venture to say many. Dempsey defeating these men despite the size difference doesn't prove he could defeat a skilled giant like Klitschko Bowe or Lewis
I don't know, quite a few I'm sure. But there's no arguing with the manner in which Dempsey did it. I mean, you could throw similar questions at any HW. For example, how many 220 pound (or less!) heavyweights could beat Berbick, Tucker, Bruno, Spinks and 38-year-old Holmes? How many 200 pound (or less!) heavyweights could beat Max Baer, Max Schmeling, Billy Conn and Tony Galento? How many 245 pound (or less!) heavyweights could beat Sultan Ibragimov, Chris Byrd, Ruslan Chagaev, Kubrat Pulev, David Haye?
I would venture to say that beating them makes his credentials more worthy to do so than Marciano's which is the real point of your thread isn't it.
The why has no 185lb fighter since then ever beaten a Fulton or a Willard? Why are these isolated incidents in the history of the sport?
I don't know about Morris .. No one ever did it before or after to Willard like that .. Fulton could clearly fight and I would not be so dismissive of him .. Firpo is way too under rated .. very crude for sure but very strong, a murderous puncher and actually pretty fast if you watch the real time punches that knocked Dempsey out of the ring ..