Yeah, it would have helped things along had it been him and not Johnson. By the time Joe Louis was champ, he was widely accepted and loved because he had a good public image. My (very white) grandpa was a big fan.
I will make one sub prediction. Whenever it had happened, it would probably not have been on American soil. The big money for title challenges for black contenders was coming from other countries, mainly Australia. Perhaps it was always meant to happen in Australia.