I wouldnt say Toney or Foreman. Toney was fat but he did spar all the time and he had the stamina, he was fat but not out of shape. Foreman also trained very hard and took it very seriously, he was fat but thats just because he was old, he was in better shape than other 40+ fighters like say McCall or whatever. He was fighting the top guys in 12 round fights. Corrie Sanders was in worse shape than either of them and really was looking for the knockout than planning on going 12.
All his cardio is swimming and not running. That's why he seems flabby. He probably could fight at 130 if he was running.
He wasn't out of shape, but Shannon Briggs was about as poorly conditioned as any champ ever. He was built like a bodybuilder, not a boxer, and his stamina really suffered for it.