Hagler, the more skilled and his chin was one of the best. Yes, JJ will definitely test that chin but Hagler will be getting stuck right in, and Jackson will take a painful beating. Marvelous stops him sometime between 5th - 7 th imo.
Lets put it this way: Hagler took Fulgencio Obelmejias', Juan Roldan's, Thomas Hearns' and John Mugabi's punches almost without flinching. Im not mentioning Roberto Duran in that bunch because while Duran is one of the top punchers of all time, a lot of Duran;s knockouts were as a Bantamweight to Lightweight, but he also took Duran's punches. Thats comparable to Muhammad Ali's run in which Ali took punches from Sonny Liston, Joe Frazier, Mac Foster, George Foreman, Ken Norton and Earnie Shavers without getting knocked out by any of those. In Ali's case, he also fought an all time hitter who did most of his work at a lower division, Bob Foster, Obelmejias, Roldan, Hearns and Mugabi had raw power and determination. Hearns, of course, had a bit more than just that. My point is, if Hagler could take shots from those four without much effort, then he could take on arguably the best hitter of all time and Jackson;s punches, in this case, would not affect the outcome that much. In a close, exciting encounter that would mimic Hagler-Hearns, Hagler eventually finds his way to a tko just as Fergy describes above.
JJ's power was shattering but his skills were not on par with his hitting. Hagler would imho take him apart because his own fighting nous and versatility was so much greater. Jackson has a whiff of Wilder about him, where high level opponents often make him look pedestrian until he drops his nuke. Hagler is one of the best chins in MW and he was in any case not in the habit of taking flush shots.
Lol Hagler too 11 round to stop John Mugabi. Jackson is way more skilled than Mugabi. Jackson also was a bigger puncher and knocked out better fighters than Mugabi knocked out. Jackson was only beat by 2 people in his prime. Gerald McClellan a guy who walked around at 190 pounds and too Mike McCallum who I would pick to beat Hagler as well. If Mugabi could go 11 rounds with Hagler then so could Jackson. Also I recall Jackson calling out Hagler and Hagler apparently wasn't willing to taste that power.
Was Hagler really in his prime when he fought Mugabi? Jackson does not have the boxing ability or defense to last the distance with Hagler. And Hagler will take his best shot if he does get hit. Here are the 160 lb fighters Jackson beat in title fights Herol Graham He was toying with Jackson but got overconfident an got caught with is hands down. His chin was nowhere as good as Hagler's Dennis Milton Decent fighter who had oupointed a green McCllelan and a fading Michael Olajide. Jay Bell Who? Ismael Negron Clubfighter who was better at 160 lbs. Then McCllelan obliterated him twice I would favor the Hagler who beat Mugabi to beat the prime version of Jackson. Mugabi fought the fight of his life and actually exhibited better boxing skills than Jackson, while having close to equal punching power. And he didn't hurt Hagler at all. The prime Hagler would beat Jackson earlier. Either way Jackson is not seeing the final bell.
Hagler never fought after the Leonard fight At the time he fought Leonard , Jackson had recently been stopped in two rounds by Mike McCallum and was fighting at 154. At the tail end of 1987 Jackson won a portion of the 154 lb title by stopping the mediocre Baek. If he called Hagler out anytime in that time period Hagler probably laughed it off. By the time Jackson was a full fledged Middleweight Hagler was long retired.
If you want to use your logic name one HOF middleweight that Hagler beat? Hearns wasn't a natural middleweight. Duran was a natural middleweight. Also was Jackson in his prime when he lost to McClellan? You do realize Jackson had eye problems years before he faced Gerald.