I'm trying to reduce this to some basic principles, in order to work out what the desired end point is, and it just falls apart. (Evidence perhaps that people who make laws are no cleverer than the rest of us.)
Women need concessions from the general rule against sex-discrimination, because of their physiology, historic disadvantage, and the instinctive privacy needs of both sexes.
Men have never objected (apart from a bit of grumbling about affirmative action) because they benefit too.
The GRA threw a spanner in the works by making some men legally female. But, because marriage, tax and pensions have all been equalised, and sex-discrimination outlawed, men and women are now exactly the same under the law, except for the concessions referred to above.
Transwomen are physiologically male and therefore women should be allowed to discriminate against them. Not allowing this is sex discrimination (because women are more disadvantaged by mixed-sex anything than men are). So TW should be treated as men when the concessions are applied, whether they have a GRC or not.
This makes the GRA otiose, because the only area in which the sexes differ in law is precisely that in which birth sex has an overriding practical effect.
( I do think there's scope for giving trans people concessions around privacy and proportionate representation in public life: these should be designed specifically for trans people and not by subsuming them into another disadvantaged group.)
(Also, the fact that concessions from the general rule against sex-discrimination exist in law, is proof that birth sex must not be concealed, for otherwise the concessions cannot be applied, so why do they even exist?)
TLDR: Repeal the GRA. Because humans can't change sex.