I would have to state a case for Bernard Hopkins. He was middleweight champion for 10 years 2 months. He only lost to Roy Jones who was in his prime. He broke the record for middleweight title defenses. Making a total of 20. He defended the belt against.

Bo James, Joe Lipsey, Glen Johnson, Simon Brown, Robert Allen 3times, Antwun Echols 2 times, Syd Vanderpool when he was actually somebody, Carl Daniels, William Joppy, Oscar De La Hoya, Howard Eastman and fought Taylor twice. Plus a few unmentioned.
He has been on the pound for pound list 3/4 of his career. Pretty good if you ask me.