It’s an interesting dilemma. The reality is race is something that can be easily seen, and U.S. history is what it is. I can see why someone would want to cast a black man as an outlaw in a western. It’s genre fiction — even though it may have come from a specific time and place, it’s not limited to it, and at it’s core there’s nothing particularly “white” about it.
At the same time, there is a basic striving for accuracy that is necessary for movies, and you have to wonder about the consequences of going against that due to the creator’s political preferences, without confronting it in the film itself. Whenever you leave viewers (or readers) with questions whose answers amount to “Because that’s how I wanted it” it’s rarely a good thing.
I don’t know. Maybe it’ll just be something people get used to, like American movies set in France where everyone speaks English.