Rule #1, the showrunner lies.
Again - I'll refer to real world politics - they are not going to a) cast the first black doctor, b) do press interviews about it being the first black doctor and then c) turn around and go "actually it was all lies" - absolute shitstorm.
It's the Doctor. The actual doctor. The real, not alternative universe, not twisted timelines, but real Doctor. she just happens to be a black woman this time.
It's not the Valeyard, it's not Susan - it's not K9 in a suit - it's the Doctor.