Hopkins comes to mind for me. Not that he was necessarily robbed (well, the Mercado draw was probably borderline robbery), but he lost just about every close fight he was in, and that's pretty rare for a long-serving champ. Did Hagler ever win a close fight? He definitely beat Vito imo and while I think Leonard deserved the nod, it was close enough to go the other way too.
Hagler didn't win any close fights. Unless you consider the Duran fight close which it wasn't. I guess you could call the Duran win a robbery for how close the judges had it when in reality Hagler was much farther ahead. Not a lot of room for him to even have close fights considering he stopped almost everyone.
Wasn't at least one of his two losses before Leonard close as well (Watts, Monroe)? All of Hopkins's losses between Jones and Dawson were close. And his draws with Mercado and Pascal disputable (haven't seen the Pascal fight, but that was the impression I've got).
Early 60's Luis Manuel Rodriguez lost 3 SD fights to Emile Griffith (LMR winning one by UD). If he wins those fights, then a case could be made he was the dominant welter of the early 60's. (FYI....a bigger thorn in LMR's side was Curtis Cokes, who he never could really figure out in their bouts in the mid-60's).
I believe the first Monroe fight was a deserved loss for Hagler. Every other blemish on his record was close enough that it could have gone his way. Marlon Starling too. The close ones never seemed to go his way (Breland, Blocker) plus the Bumphus fight which went to a TD after seemingly being stopped on Lou Duva's say so.
I saw the first Monroe fight on CCircuit. Thought Hagler lost the fight. Hagler was still on the way up..and could be "outboxed' at that stage.