Hagler's 2nd loss, to Willie Monroe, wasn't controversial. From what I've read, it was a clear loss. Haven't seen his draw against Seales, but I saw the loss to Watts and that was bull****. I don't see what the judges were watching, but Hagler won that fight. Judges weren't always so nice to Hagler. The loss to Watts, draw with Vito, overly generous cards to Duran when they fought....Leonard winning didn't bother me that much, but the 118-110 card was disgraceful.
I don't think it hurts his legacy at all. Simply out, the big money fights out there to be made usually involved smaller guys who were terrific fighters moving up, like Leonard, Hearns and Duran. It made sense to fight them. Even at that, Hearns may have started out a welter, but he was closer to 154 or even 160 in actual size, given his frame. He even competed at cruiserweight. Leonard also competed at higher weights like 168 and did well, even as an older guy. By the time these guys fought Marvin they were definitely proper middleweights, and not blown-up welterweights. Duran is the only exception, being naturally a fair bit smaller than Hagler. Yet, he beat the snot out of Dave Moore at 154 and also beat the tough Iran Barkley at 160 as an old man. Duran may not have been a natural middleweight, but he was good enough to make life very uncomfortable for some big names. You're right in that Hagler was probably a bit too cautious against Duran, but Roberto was such a clever fighter that if Hagler got too aggressive, he may have given Duran more opportunities to counter him. Look what he did with an aggressive Iran Barkley when he was 37. It was not a perfect gameplan by any means, but Hagler got the job done and that's what counts ultimately. PS-Hagler wasn't a big middleweight. If he's lucky, he stood 5'9". My dad met him when Hagler was out here in 1980 for the Coetzee v Weaver fight, and he said Hagler was smaller in real life than he looked on film.