I think he could win or lose to any of them. Resumewise Robinson has unmatchable stats but abilitywise, I think he fits in right among Duran, Hearns, Hagler, and Leonard. Hearns could clean Robinson's clock or box him and would be hard to hit with his range. I think Leonard would be a tough fight as well because Leonard was so tough, fast and precise. I think Duran and Hagler could both be tough fights for their boxing skill and durability alone honestly. I would be surprised at 0-4 for Robinson, but I would be more surprised with 4-0. Robinson still has the best resume but on film I think it's plain to see how he could potentially lose to these equally talented fighters.
At his best he beats them all, knocks out Duran, too big, knocks Hearns out, too powerful for hearns chin, outboxes Hagler in a war, has a bit too much for Leonard and wins a decision
Robinson whips Duran and Leonard but probably loses to prime Hearns who peaked at 154 then loses to Hagler who is too tenacious even for Robinson Hagler & Hearns then face one anotherfor the top p4p ranking and Hagler stops Tommy in a real war
I genuinely believe, and have said for years on this forum, that a primed SRR is a perfect blend of the best of Leonard and Hearns. He has the right hand power and can fight tall like Hearns, combined with the punching speed and versatility of Leonard. SRR can do a Hearns job on Leonard but when Leonard goes to the body and tries to macho SRR, SRR is a lot more durable than Hearns was and fought back ferociously - a bigger puncher than Leonard. SRR is better with the body work than Leonard was and could keep his man at range. I don't like Duran's chances against SRR. I don't envisage the knockout that Hearns got - but I do see Robbi hiding the right hand and landing similar bombs. Robbi stops Hearns quicker than Leonard did if in the mood for a tear up. Hagler was a greater MW but this would be his biggest fight ever. He cannot just jump on Robbi like he did with Hearns. Robbi is more durable, a better infighter and if he does decide to box and move, Hagler's tentativeness against Duran and Leonard, at times, don't bode well against someone that can move and box, with the handspeed and turn on a penny punch power like Robbi. I could equally see reasons why they could beat Robbi, but at his best, primed to fight, I would favour Robbi to beat them all.
You would have to favor Robinson against all of them. Leonard and Hagler would fare the best. Tommy Hearns would not have been strong enough for SRR. I see him getting taken out very quickly, he was too chinny. It depends what year Robinson fights Hagler. If it's the Basilio era, then Hagler could pull off the win. If it's earlier, then I take Sugar Ray, but in a tough fight. For some reason, I always thought Robinson would have a tougher time with Hagler then Leonard did. Different person, different approach to fighting. Robinson liked to slug more, where as Leonard would not do that. There would be more fireworks and this could make the fight harder for Ray than some would think.
4-0 Hearns gives him the toughest matchup on paper. Robinson would fight Hearns like he was double parked. Sugar Ray gets him out with that quick lefthook. Duran could slip inside like he did in Montreal but he might not find a firefight with Robinson all that much fun. Sugar Ray wins a 10-5 decision. Leonard would be interesting. I honestly don't know how RL would approach this tactically. He's outgunned toe to toe, that lefthand of Robinson had a life all it's own. He could move but they were equally fast. Almost want to say he would fight inside vs Robinson. Leonard was better inside than SRR. I don't he could apply that enough to win though. Sugar Ray decision. 10-5. Hagler would have trouble with SRR's speed and versatility. Robinson was a true middleweight especially in his punching power. Anytime before his initial retirement Robinson cruises on points.