Can’t really say in history but I always found Guillermo Rigondeaux to be overly cautious. Some people label it as “defensive minded” fighter but it’s not. Mayweather jr was defensive minded to me, but Rigo seemed afraid at times he shouldn’t have been. Tough question... kudos!
Mayweather Jr. He could of won fights far more emphatically but never liked to take the chance he might get caught
Post Baroudi Ezzard Charles could slow a fight to a complete standstill if he needed. It's one of the reasons why he was very unpopular.
Wlad Klitschko is the one that frustrates me the most. He would be pecking away at a guy he could have blown away 4 rounds earlier, just in case there was still the ghost of a shadow of a chance that the guy had something left in the tank and might hurt him. For every crushing performance he'd have a snoozefest to balance it out with.