It's been happening since he took over and he admit to that. But not only did he keep drip feeding the idea, but he also changed the shows dynamic to the point where the BBC felt it needed a change like this to make it interesting and increase viewing figures. Before Moffat, characters were believable, consequences were present, and the companion was very much the lead of the show (along with all the other things that changed with Moffat).Just to make sure there's no confusion here... If fingers need pointing, then they need pointing AT Moffat, not Chibnall. Yes, Chibnall presumably was the one who had ultimate power over the casting choice, but Moffat spent most of his time as showrunner first drip feeding, then full on pushing his female Doctor agenda, ever since "The Doctor's Wife" with the line about the Corsair's multiple genders, leading to Missy.
Despite the gist of the above, I am trying to keep an open mind...