Styles make fights. Barkley was tall, strong and powerfull. He was able to get inside of Hearns reach and tough enough to take punishment on the way in. It helped that Hearns' legs were not very good by the time Barkely got to him and that his chin was suspect.
Barkley was just an awful match up for Hearns, he was too strong, so Hearns never found himself in position to throw and when he was he would get hit by Barkley's hard shots.
I remember Hearns landing body shots that made me wince just watching them and Barkley soldiering on... Iran didn't have a slick bone in his body and was prone to bleeding (think he got busted up in this fight). Tommy would have been better served boxing and trying to carve him up for 5 or 6 rounds before unloading the power. But Iran was a true warrior. All the respect in the world for him.
Stylistically. Hearns had a shaky chin. Barkley a top chin with true middleweight size and good power.