No clear answer for this because we have insight on the more popular fighters, more footage, more articles. But we don't know about other less popular or less successful ones. Many of them probably work their asses off but still don't reach a high level.
Gotta include both of the Klitschko brothers. 93 combined fights, over a total of almost 28 years, and they've been in shape for all of them.
Are you serious? First off, he's not active. Second, do you really want to list a cokehead as one of the most disciplined fighters? Not only that, but he wasn't all that disciplined in the ring either. He was a great fighter none the less though.