Rocky in the modern world, would be a Cruiserweight, his best weight and average was around 187, so today, or against most of those guys mentioned, it would not be a fight with him at 187, same for Jack Dempsey, he was a cruiserweight and with their height, that's where they belonged, so just to even discuss the fact that they could have beaten the top 10 heavies of all-time or even be one of them is amazing.
Ali fought his best at around 220, and he was tall with a reach, with his skills, I could not expect the greatest Cruiserweight of all time to last with him in his prime.
