I don't think it would be a slugfest but what it would be is Hagler lacing Barkley whether he came forward or tried to "box". If he held off Hagler would come forward with the jab and counter the heck out of him. If Iran came forward Hagler would employ some lateral movement and counter the heck out of him. Worth remembering Scypion was a shell of his best when Barkley fought him so it was a lot easier to look good against him than in years previous.
I think it would be a heck of a fight and prefight with these two guys. But Marvin was just too versatile for Barkley. Barkley had the style for Hearns, but he really was not a great fighter. He beat a great in Hearns because of style and he fought another great Duran and some hall of famers.