It sure would have been a classic, Archie Moore was a defensive master. That left hook that Sugar Ray Robinson used on Gene Fullmer was fast and deadly, Fullmer needed help back to his corner.
Quite a few- Saad Muhammad, Marvin Johnson, Mustafa Muhammad, Qawi, Spinks, Foster, Moore.... Robinson was a great welterweight and middleweight, I don't see him ruling at 175 though.
Robinson was great but too small for a great light heavyweight. Even a good light heavyweight contender with a big punch would be dangerous.
Especially since his prime was as a welterweight. Even against a Marvin Johnson or Matthew Muhammad type who were very, very good but not ATG, he would be in deep waters.
Beterbiev, Michael Spinks, Michael Moorer, RJJ,... and the list doesn't end there. That's why there are categories, and the SRR didn't come close to the rehydrated 175lbs.
Much more than you think - frame doesn't lend well to moving up from 147 to 175 lbs, not when he's probably a natural 154lb fighter. The nightmares of Doyle compound the issue for Robbie. Still the GOAT tho