I think people missed my point. Doctor Who, and television entertainment in general, should not be an exercise in political correctness, it shouldn't be turn taking, and we shouldn't be sitting working out what percentage of the characters are what. This is supposed to be entertainment, the telling of a compelling story by people experienced in doing so, on either side of the camera.
It's like fair employment. A person should not get a job, or be denied a job, simply because of quotas of "how many of your sort we already have".
Take Journey to the Centre of the TARDIS as an example. Yay, we have 3 black brothers running their own business. But can the actors act? Hell no, they were awful. They weren't awful because they were black, they were awful because they were bad actors.