If Hearns can box, he wins. If Johnson can force a firefight, he wins. Either man could lose based on his lack of stamina and durability. But due to being bigger, I give Johnson an edge, so I have him with a knockout anywhere from 5-11.
Johnson is the wrong kind of light heavyweight for Thomas Hearns, but the Hit Man has a chance if he boxes patiently and smartly and uses that jab to bust Pops open to try to force a win on cuts.
Yesterday I read the original post and was about to say Hearns by KO. Then I realized I was remembering Hearns at 147 to 160. I don't think he was nearly as effective at 175. Johnson was stopped by the best in the division- Spinks and the two Muhammads. I can't extrapolate from those fights that Hearns would do the same. Pops was fabulous against Galindez and Parlov. After thinking about it, I'd go with Johnson by stoppage, maybe around the tenth round.
Thomas Hearns though very talented, good boxing ability, good mobility and a very destructive right hand would not be able to keep a very aggressive Marvin Johnson off of him. Hearns may be able to survive the first few rounds but Johnson, who is a natural 175 lb fighter and a southpaw, would wear down Thomas enroute to a 10th round stoppage.. Johnson has faced the likes of Victor Galindez and Matthew Saad Muhammad before.
Hearns was a top 20 pfp ATG imo. But Johnson was a full-blooded light-heavy, three-times champ, with one heck of a lot of heart and an actual light-heavy punch. Hearns would have been overwhelmed in 4 I think, at the most. I think Thomas would have been frustrated seeing Johnson take his biggest shots, the kind that knocked Welters and Junior Middles silly, and still keep throwing certified light-heavy power shots.
I do think Johnson's power would be too much for Hearns, but I think that Hearns becoming a light heavy later in his career could make it appear as if Hearns wouldn't have made a great light heavy in his prime. Idk, but it's worth mentioning.