Ellis was more of a natural light heavyweight than a heavyweight. IMO although he had real success at heavyweight, he might have been a top 10-15 ATG light heavyweight if he fought at that weight.
Over eighteen months or so the man went from fighting at 160 to fighting at 190 and challenging heavyweight contenders .. he was a middleweight for much of his career .. fighting and losing to Hurricane Carter and George Benton .. not sure what motivated the move but his career had a reboot and he had a terrific run in a era of Ali and Frazier dominating .. it can be argued that Ellis was the third best heavyweight of that period .. he beat Martin,. Bonavena, Quarry, Patterson (decision dicey but he did get it ) and Chuvalo .. I'd have loved to see a prime Ellis fight Foreman .. he very well may have surprised Foreman 1 ..
I dont know that Ellis was really a natural middleweight despite fighting there. If you look at those fights he was as raw boned as it gets. Zero fat and not much muscle either. He didnt look healthy at that weight at all. I suspect the decision was made there because he could boil down to 160 and they hoped, given his size, that he would have an advantage over the natural 160 pounders. When he moved up he was a much better fighter. In a year and four months he put on 32 pounds and I doubt he was taking steroids. That tells me he was really killing himself to make 160.
Some people look very large and bulky despite a low weight. It's about genetics. You can also have a guy be very lanky but deceptively strong (wiry strength) I've met several examples of both in person and it does throw you off. As for Ellis gaining weight, he wasn't exactly this shredded muscular dude nor was he fat, so I'm inclined to think it was natural progression and not Peds. It's not like his performance suddenly became 10x better with a huge spike in stamina or strength.
He certainly had more success at HW. That usually isn't the case when you move up that much. Most often fighters have less.
Could be although he was about 25 or so when he moved up and was always kind of soft looking at 190 .. that said no doubt he went from a drifting middle to an alphabet champ at heavy so the moved certain helped him ..
he had power, great sneak right Jimmy Ellis whipped 5 ranked heavyweights in a row Johnny Persol Leotis Martin Oscar Bonavena (2 knockdowns) Jerry Quarry Floyd Patterson very few fighter's in any division ever fight five world ranked guys in a row, (ALI) Jimmy was also to defend his title in 1969 Peralta, Cleroux and Cooper.
Ellis hadn't tasted the canvas as a heavyweight until he met the fists of Frazier. He took Quarry's best shots. As well as Bonevena. Pretty solid chin.