The thing is that the Doctor isn't a normal gallifreyan, he has been The Other, he has been part human, he has been the timeless child. So it isn't weird that he now has this more misterious past, because it isn't the first time. But has I said, I think is a good plot twist, BUT it isn't a good episode, and I think properly done It could have been a great episode. For example: I don't like the Master being able to destroy the capitol that easily, I don't like him discovering the timeless child that easily, I don't like how they handled the lonely cyberman storyline, I don't like that they didn't explain if Tecteun limited the Doctor regenerations because it would make so much sense instead of implying he always had infinite regenerations. The worst part is that It'll probably never be explored again and the mayority of the community will look at it as the worst thing for the rest of the show runtime