Looks cool but it seems to me if you are going to film an origin story about Dr Strange you would at least need the Ancient One and Baron Mordo. If they can't even be bothered to cast those roles properly, why even bother to make Strange a middle aged white dude?
It is tiresome. And it's been explained. These characters were invented back when racism made diversity impossible. Disney/Marvel is using this opportunity to correct that error. They also hope to appeal to a wider, diverse audience for better financial success. So when the opportunity presents itself to cast someone as something other than a white male, they take it.
Strange, Stark, Thor - those characters are iconic. Casting against ethnicity doesn't fly as well in those cases (see Johnny Storm in Fan4astic). So you pick your battles.
If Mordo being black gets your panties in a bunch, I feel kinda bad for you.