Successful art doesn't have to be accurate. Successful entertainment even less so!
It's super telling that you get people essentially complaining about AAVE like it's an existential issue for the movie, but silence on any other anachronisms not related to race.
Denzel played a great Macbeth in the recent Joel Coen movie, despite not once being Scottish. Acting!
If you're doing an artistic thing, fine. But I'm really getting sick of virulently racist eras being portrayed by a multiracial cast becoming standard. 20 years from now, young people may not even understand what the problem was, never having seen a depiction of racism, and watching black Scottish kings, while the descendants of slaves will still be living in the gutter with about the same wealth that we were released from the plantations with: zero.
If racism is a 'was' in 20 years, I would be happy to take the win.