A lot of interesting matchups vs Hearns, but at Welter Tommy is a monster especially head to head and quite unusual in what he had to offer. Robinson is the most comfortable choice to beat him from me. Guys like Griffith, Gavilan, Burley and Walker are good shouts too.
As others have said, Hearns was very vulnerable. The painful truth is he lost all the big fights. Yes, I know he hit hard, he was tall, his power, height and reach could give anyone a hard time, but Hearns was a let down in the real big fights. He had a chin/stamina problem. Ironically, I think he would have a good chance against Mayweather... maybe because I don't think Floyd has the punch, nor the desire to really go after Hearns as Leonard did.
Not that many WWs can hang with Hearn's power, height, reach, and boxing ability. Fighters would need to have the size, speed, power, toughness, and killer instincts to reach in to Hearns' fragile chin but will have to get punished in the process and not many can handle that unless your first name is Sugar. Sugar Ray Robinson would be the only fighter that I would confidently pick against WW Hearns. The only other WW that I think might have somewhat of a chance against Hearns would probably be Donald Curry or Marlon Starling, but that's very slightly. Curry and Starling did beat tall lanky fighters with power (McCrory and Breland) but they were obviously not in the same level as Hearns.
In Duran's autobiography he states he was cautious of drugs. He was quite a drinker, though . I think he used them atleast once though, just my view, and the period before Hearns would probably be the time, as before the bout he was out 'partying' with Lesbian couples (really) frequently, bringing along massive bags of money. Also, the '80s.
He was 33 years old fighting @54. Not exactly his peak. Did Duran look the same to you? Compare him to 28 years old against Palomino or Leonard. He had good speed in his prime. Non stop motion.
Trinidad would be a very live dog. He was a huge Welterweight himself. Hearns would have to be the Hitman here or he might get stretched himself. If he lets Tito get into the middle rounds it becomes a serious fight. Trinidad had great two handed power at 147. He wasn't exactly slow. Tito could conceivably get off the canvas to win. Hearns wouldn't.
Griffith kept punching from to far out like Khan did v Bud where he fought Monzon, Hearns reach and power would be too much for Griffith who kept over reaching v Monzon and falling off-balance. Nobody with arms as short as Duran`s would ever have beaten Hearns.
Bud would have given Hearns hell, he`s got more power combined with reach than most guys Hearnss fought at 147 and he`s a hell of a counter puncher, Tommy might make a mistake like he did v Ray.
Tito was a sucker for the jab as Wright proved ,Hearns could jab his face off without trying for the ko.
Crawford's overrated. Hearns has his head in 5. Spence would be a tougher challenge. Although even that could look like the Cuevas fight
Winky was a totally defensive minded fighter. + Southpaw. Hearns had lapses in his defense and not the best recovery abilities. Trinidad was too dangerous to let hang around. Hearns should/would be the favorite but he could end up staring at the ring lights himself.