What if Hearns had boxed Hagler? Leonard did win the fight by outboxing Hagler in my opinion. Hearns had some success boxing Leonard.
He was going to box Hagler but Hearns had no chance, because Hagler jumped on him like a rabid dog. And gave him no chance to use his reach or boxing skills. Hagler even said he deliberately jumped on Hearns early so he couldn't use his reach, remember Hagler was more of boxer/puncher. It wasn't the norm for him to come out as aggressively as that, so obviously that was the gameplan for Hagler. And of course he was confident in his durability to outlast Hearns in a war.
Hagler turned into a bull for this fight and was all over him. Hearns had to try to get his respect. When he tried to get some distance in the first round and stay in the middle of the ring, Hagler was able to cut him off and get him on the ropes. Hearns tried to use more movement from the 2nd round on, but Hagler would keep getting to him.
Not only was Hearns extremely hard to outbox at long range, but he was most dangerous with the right hand when he got distance. The knockouts over Cuevas, Duran, and later Shuler were when Tommy got some distance and more leverage on the right hand. So I’ve always thought Hagler’s plan to swarm Hearns worked in multiple ways.
If Tommy started out boxing, Hagler would box him back. Also that cut Hagler sustained would have happened a lot later. Hagler is a more fundamental boxer than Hearns with a better implementation of the jab in my opinion. Hearns had a long jab but would often have his hands very low while throwing in volume. Hagler would find that opening and force a fight.
I think Hagler would have found his way to the inside regardless had he opened more cautiously, and obviously Hearns was able to brawl, but Hagler decided to not let him have any advantage in regards to jab/reach which probably slumped Hearns' confidence a bit too