Interesting question. He might have been. Ray Leonard had celebrity status in the 1980s. And I’m not sure how many non-heavyweights prior to his time had that.
Ray Leonard was the first to bring Heavyweight purses to the lower weight divisions. If that is an indicator.
Probably in America? In Mexico, Korea, Panama, Australia and Japan your mileage may vary. World wide overall? I don’t know how to answer that but I think yeah it’s probably Leonard or Robinson… late career Robinson… not so much.
The OP specified non-heavyweight, and Ray Leonard would be a strong contender for this - Ray Robinson was popular in his own right, but Leonard commanded insane purses, and had media attention like few boxers, heavyweight or not, before him. My perspective is when someone from the general public with no interest in a sport can name the athlete - say, Gretzky or Jordan. People with no normal interest in hockey or basketball know these names. Ray Leonard was one of those athletes, and maybe one of the first "smaller" boxers with that level of fame.
I think it might have been Stanley Ketchel. He had a fan-friendly style, was a great white hope for a while, and Jeffries was retired and Jack Johnson was not a popular champion...but how do you measure these things?
