Ray may be the answer to this thread question. He also may be the guy who got the most out of his fights. In just 40 career fights he won championships in five weight classes, beat four different all-time greats and fought an overall high level of opponent from his 14th fight on.
Leonard is definitely a candidate. But it should be noted that James Jeffries retired with 20 pro bouts and won the heavyweight title with only about 11 bouts. Along the way he beat two greats in Fitz and Corbett and only lost once to a future great after a six year retirement. Now to clarify, Ray Leonard is a higher caliber ATG than Jim Jeffries. But Jeffries still qualifies as “ great “ and had far less fights than Leonard
Joe Frazier had a career total of 37 fights and beat Ali with a record of 26-0, which was his ultimate prime.
Oleksandr Usyk has had 20 fights and if he retired now he’d be a consensus HOF’er. He probably achieved “greatness” (its a subjective term) after unifying against Gassiev in fight 15. He definitely deserves a shout out. His resume is ridiculous with or without Fury on it. Holyfield is very similar but I think Usyk was matched even tougher earlier and that’s saying a lot because Holy came up as hard as anyone.
Jeff Fenech won a world title in a third weight division (when that was still a rare achievement) in his 20th fight. You could argue that he established his greatness with that win.