I miss some diversity here
Sam Cooked could have been played by an Asian actor. Since Hollywood always cast the same Asian actors again and again, either Donnie Yen or Jackie Chan would be a good cast.
Malcolm X could have been made gender fluid, bringing out his secret identity as a black transwoman which led her to choose the X as a symbol of the chromosome that truly defines her.
Muhammad Ali should be played by a Muslim Arab. No need to say that casting a non-Muslim to play a Muslim is a huge offense! Rami Malek, maybe?
And finally, a latino Jim Brown. Male or female, please let's not be sexist. We need some gender diversity too! Michelle Rodriguez would have been a perfect cast!