Only fight I remember Hearns being the "heel" would have been against Leonard. And that's not unexpected. I'm a bit too young to remember the behind the scene narratives but I didn't think Hearns was a heel against Hagler and I was rooting for Hagler. Same for Duran or any other big fight for Hearns.
My memory of Hearns was that of a long, lanky kid always getting in to the ring against physically stronger fighters.
Hearns had that Bruce Lee like power. Summoning all his muscle with each punch. He just had gifted power if you will.
I thougt he fought Ray too early, but nonetheless he messed up Sugar Ray's eye forever. Had he had waited a year or so, and gained some distance (late round boxing) experience he would have been unbeatable. I followed his whole career and saw greatness very early.
With that said Marvin Hagler kicked his arse. Hearns went up in division and paid a price partly because big boys hit harder and can take little boy's punches, at least until the fighter adjusts to the new weight class.
Goes to show you the level and number of great boxers back in the days.