Yeah I’d take Robinson via clear decision. The hand speed, movement, and combination punching get it done via competitive but clear decision in an ugly fight.
The Robinson that beat up LaMotta would most likely have his way against a great fighter like Monzon who is notably much slower and methodical. Robinson’s quicker hands and footwork, along with his deadly combinations may be a nightmare for Monzon.
Despite his immense speed advantage; I like Monzon here. Robinson was a great ring general; but Monzon's was better. Robinson traditionally struggled against those who spoiled his work and didn't give him space. While Monzon is hardly going to rush at him and grab on like LaMotta, Angott or Zivic did; but he would likely use his longer arms to stifle Robinson's work. Holly Mims had success doing similar, too. Plus, Monzon's only really struggle in his title reign were against Griffith and Valdez. Neither fought like Robinson, and both used a quality Robinson didn't have. They were just - or at least almost - as strong as Monzon. Robinson wasn't, and his blistering bursts wouldn't make up for it IMO. If anything, they'd get him caught and tied up again. After a messy few rounds early on, I think it'd become a story of jabs, and while Robinson's jab was excellent, he didn't stick with it like Monzon did. Robinson would get fiesty and it's cost him IMO. Monzon by ugly decision in a close fight.