Since people like to bring up Nonito Donaire only looking good because he had the slight "size advantage" in the lower weights I'll give you a list of other fighters that have done the same as well. Thomas Hearns Gerald McClellan Ricardo Lopez Alexis Arguello Oscar de la Hoya Arturo Gatti Diego Corrales Paul Williams Antonio Margarito What are some other fighters you can think of that always looked bigger than their opponents?
Broner comes to mind. He was massive at 130 and even 135 but jumped up too quick and got found out at 147 and hasn't looked nearly as good at 140 since either.
The difference is most of those guys could beat down other guys their own size. Donaire just got beat down by a guy his size who wasn't as talented as he was.
Historically the champ tends to be bigger than the rest of his division. The guys who are considered the best punchers or the most dominant usually have abnormal height and reach advantages, ie they belong in another division. I usually cite Tommy Hearns, Ray Robinson, Alexis Arguello, Paul Williams, Bob Foster, Michael Spinks, and Bernard Hopkins as prime examples of this. This was also a major factor in their ability to climb weight classes, since they usually just moved up to weights where their height, reach, and punching power were normal, as opposed to true p4p greats like Roberto Duran, Mickey Walker, or Henry Armstrong who were undersized for the divisions they fought in.
Ali was 6'3" with a reach of 78" and weighed about 215-220 in a time when the average heavyweight was 6'0"-6'1" with a reach of 74" and weighed 205-210. The heavyweight champ is almost always the biggest guy around, with some notable exceptions. Joe Louis and Mike Tyson might be the only dominant champs who routinely fought guys who were bigger than them. Dempsey gets credit for beating three guys bigger than him, but their skills or condition are debatable. But there is a reason why Jack Johnson was only six feet tall but called the Galveston Giant. He took the title off a guy who was five foot seven for Christ's sake! Ali definitely had size advantages against most of his foes. Jerry Quarry, Ellis, Frazier, Floyd Patterson, Sonny Liston, Oscar Bonavena, Chuvalo all smaller. But he did fight a few guys who were as tall Young, Holmes, Norton, Mathis, Lyle, or bigger Bugner, Foreman, Terrell.
Ali compared to Marciano:http://i23.photobucket.com/albums/b374/ROOFIEREEFER/marciano-ali2.jpg Ali was a big man for his day
How did Hearns and DLH make this list? They certainly used their size to their advantage when they were younger, but they both had success as they moved up. To be fair, the same can be said for Donaire. Keep in mind that the guy started out as a Flyweight.
That doesn't in anyway contradict my statement. 39 of Ali's 50 opponents were or had fought under 200lbs.