Duran, Hearns and Hagler. What other fighter can say they have three wins of that quality over non-shot fighters? Ali has Frazier, Foreman and Liston. That's insane too but I think Leonard's are better.
3 great wins for sure, particularly Hearns 1. Durans win over Leonard may be the single best win ever though
Greb has Tunney, Walker, Gibbons, & Loughran. & Bivins, who himself has Charles, Moore, & Burley on his resume.
The names on paper, and the times the fights happened makes you think yes indeed Leonard has 3 absolute insane wins, 3 GOAT worthy. But in context, Duran basically came to the fight straight from the sauna trying to shed the weight he gained from the greatest party binge of his life filled with beautiful women and alcohol, and a lot of folks feel strongly that Leonard was gifted the decision against Hagler. Hearns is the only true great win