By established, you mean they announced it this season. No, that's not Dr. Who; it never was.
Actually, the first mention of Time Lords being able to change gender was at the end of Season 4, when the Doctor regenerated from David Tenant to Matt Smith, and he remarks, "I'm a Girl!" and then grabs his Adams apple and realizes he's still male. This was in 2010.
in Series 6, when the Doctor mentioned another Time Lord named "The Corsair" who had changed genders during the time the Doctor had known him/her.
And obviously, you have the Master (a long established character) regenerating into a female form in Season 8, which was in 2014. The previously established character of the General regenerated into a woman in Season 9, which was in 2015. So your argument that it wasn't established until this season shows a lack of knowledge of the show's lore.
The fabric of the show matters. You dismiss it to play politics, you have no integrity. It's disrespectful to the fans. I was watching a story arch, not a glorified version of CNN.
I don't see how that changes the "Fabric" of the show. I think what bothers you is that it will change the dynamic. Before it was mostly female companions asking the dumb questions and needing to be saved by a male doctor. They really haven't announced companions yet, so we can assume the next companion is going to be male. It hurts their masculinity if a woman saves them?
Now, there's a lot of reasons why this could be a mess. Whitakker might not be up to the role, it's actually a tough character to play, and we've had some awful actors in it. (Anyone else remember Colin Baker?)
It might also be that they have run out of ideas. HOw many times can the Daleks or Cybermen show up and still be interesting?
Your problem seems to be that you are terribly upset that it's a woman to start with, not that this may or may not be the best actor for the role.