He's a necromancer, not a negromancer!
In all seriousness, so many Western fantasy movies are overwhelmingly pseudo European that it would be a sea change to have an actor if color portraying a major role.
Besides, if we are not allowed to play certain roles because of political correctness, then how far have we really come? In my community, actors who portray buffoons are often criticized for doing so. But, IMHO, black actors won't truly be the equals of their peers until they can portray buffoons without being called to task for it.
Besides, villains- especially educated ones- get most of the good lines.