Now, Chibnall's writing is mediocre at best, but that wasn't the only problem. There's an intrinsic problem with genderflipping. I've seen a couple of other productions that used it, and found them problematic.
Twelfth Night is my favourite Shakespeare play. In a subplot, the pompous steward Malvolio offends some other characters by spoiling their fun. In revenge, they forge a letter from his employer, the Countess Olivia, claiming that she's in love with him, trick him into wearing yellow stockings and cross garters to impress her (he looks ridiculous, and she hates that style to start with) and convince her that he's gone mad. (Note, Malvolio claims to be a Puritan, the Puritans wanted to close down theatres, Shakespeare's audience would have seen him as the bad guy).
I saw a production of Twelfth Night at the National Theatre, with Tamsin Grieg as a genderflipped Malvolio. Portraying Malvolio as a woman made the prank come across as unpleasantly homophobic. Worse still, the yellow stockings and cross garters became a yellow corset with propellers on the nipples - not merely stupid but degrading.
I also saw a production of A Midsummer Night's Dream in which Lysander was portrayed as a woman. Again, Egeus' opposition to Lysander marrying Hermia became implicitly homophobic, not merely putting his paternal authority over his daughter's happiness. The production couldn't resolve that problem, because it was never in the text - they had created it themselves.
So back to Doctor Who. Chris Chibnall presents the 13th Doctor as a great leap forward for the representation of women, but that's sheer hypocrisy coming from him. Steven Moffat wrote compelling female characters - Clara, Amy, River. But 13 is a vapid chatterbox who spouts inane platitudes and corporate slogans, Yaz is just bland, and Grace was fridged in the first episode. Chibnall has always been a mysogynistic writer - his writing for Torchwood and Camelot shows that, so he doesn't get to call anyone else sexist when they criticise his worthless gimmick.
If you want good female characters, write them as women from the outset. It worked for Dana Scully, it worked for Emma Peel. If you want good male characters, write them as male from the outset. It worked for The Doctor. But if you gendeflip an established male character (nobody would suggest doing it the other way round) you're just replacing a good male character with a poor female one, plus some awkward subtext.
