That wasn't clear at all clear given that you referred to white actors in black roles, which, thankfully, isn't really a thing anymore.
I know nothing about the teacher character, but the other examples you note remind me of the criticisms that Helen Mirren and Cillian Murphy have received for playing Jewish characters. I myself am not sure how I feel about such cases, since the actors in question are not necessarily "wrong" for the part as far as their appearance goes (Cleopatra was ethnically Greek, and plenty of Persian people are light-skinned).