Darnell Boone seemed to give most of his opponents major issues. Marcos Maidana as well. Right now I'd say that Dillian Whyte fits that mould at heavy.
Wayne " Pocket Rocket" McCullough - Guy had granite in his chin, and never stopped throwing. Always a tough opponent.
Not sure he gave Bowe or Foreman hell but they were both 30-50lbs naturally heavier. Similar sized guys like Holyfield and Moorer had to dig deep, though, so I do agree wih you, given that many others rightly listed so far would give a fighter hell in and around their natural weight class .
I'd be an impostor die-hard if I felt Bert gave Foreman or Bowe anything other than a cakewalk. You're spot on. But the way he dropped Moorer, Rocked Holy , swolled up Mercer's face like a balloon which imo was the 90s version of Foreman-Lyle. Two HWs throwing leather only Cooper-Mercer took it the distance. Under rated HW brawl and accurate at that! Anyone who went to the HW title...all roads led to Cooper, so sad his nickname was also his past time, lol!
A great call Al he could go in with anyone and hold his own. His list of opponents is extraordinary. They breed them tough in Scouseland!