I'm not reading all that now but I'll have a look tomorrow. But in response to this: "It’s worth examining why the moderates are peeling away, falling silent and joining the wrong side though, no?"
But honestly I think it's quite simple. Many of the left wing feminists who were involved at the beginning like Ruth Serworka had established social positions, identities and social circles, as left wing activists and trade unionists and realised that association with someone like Posie Parker was toxic to that and have been appalled by collaboration with the far right. I don't think they have changed their minds so much but perhaps they were those with more genuine concerns whose involvement in the movement was not so overtly driven by transphobia. But the cost of being publicly associated with the movement now outweighs the benefits.
When it comes to those pulled to the extreme sides of things I think they are terrified of the wrath and shaming of the Posie's of the world. That seemed to happen to Stella O'Malley from Genspect when she came out with some stuff the extremist transphobes didn't like. They tore her apart, accused her of being a groomer, misogynist, risk to children etc etc just like they do trans people and the result was a fawning discussion with Posie Parker where she prostated herself before her and couldn't praise her enough. I think this group are new to campagning, have formed strong social attachments to others in the movement, have often lost friends and family on the way due to the obsessive nature of the movement and are terrified of being expunged. Gender critical social media pile ons are ruthless and relentless, they get one taste of that and soon fall into line.
A third dynamic perhaps is that as the movement has veered towards more overt and open transphobia it has pulled in the right and far right which has massively increased attendance at demos, crowfunding donations and online support. The gender critical movement has moved from a small number of feminists from the left, predominantly in conflict with other sections of the left, to a mob, largely made up of right wingers and men who have the muscle, both literal and metaphorical, to start winning things like the Bud Light furore in the states and inciting the Tories to first drop self ID and then trash it in Scotland. And some old school feminists, like Julie Bindel who isn't aligned to anyone and likes attention, seem to accept this as a price worth paying.