I think that there is a very strong case. He dominated arguably the strongest division in the history of the sport. It was a division populated with great fighters, probably at the time when the global talent pool was at its greatest. Depression era America, was a bit like a bigger version of Mexico in boxing terms.
I believe so. I also believe he may have been the most dominant that a fighter has been vs. a consistently high level of competition.
I'd add Ali and Monzon to the discussion if we're talking single weights considering how many great fighters they beat at the weight