The 1972 Dolphins are considered one of if not the greatest NFL team ever, though every modern team is better in absolute terms. Jesse Owens is considered one of the greatest sprinters ever, despite hundreds of high school students beating his best times. Issac Newton is considered one of the greatest scientists ever (tied with Einstein when physicists vote on the physics GOAT), despite any 2nd year physics student today knowing more about physics and calculus than he ever did. Same for Darwin.
The point is, greatness is measured by how you do against the best of your time, not how you'd do against the best of modern times. Though I like the idea of being able to walk around claiming I'm a greater scientist than Newton and Darwin -- unfortunately anywhere but Sherdog people would say that's ridiculous, as only on Sherdog do people think greatness is relative to the best of today rather than the best of their day. On Sherdog though most of us are greater scientists than Newton and Darwin, greater mathematicians than Archimedes (for some reason actual working mathematicians think he's one of the greatest).
The number of successful defenses is one of the best indicator of how good someone was, just as the number of Olympic gold medals or Grand Slam tennis wins or NBA MPV's are great indicators of greatness. And I think actually you at least partially agree, or you wouldn't be saying respect to him -- why respect him if he wasn't great in his day?