I think the Comics Code also played a big role to discourage creators from including African-American leads in the 50's and early-mid 60's, when most of these IP's were first created, as it had forced a ban of the EC Comics story Judgement Day simply because it featured an African-American protagonist.
So who knows... maybe some of these changes could have been the original plan all along, but not possible at the time due to unpredictable protocols and legal pressure.