The law isn't as much as an ass as it seems.
The intention of the GRA was to protect transsexuals. If GRS wasn't such a brutal process, it's entirely possible that a GR certificate would not have been issued unless surgery was completed. Instead it was recognised that it simply wasn't humane to insist on GRS because some people physically wouldn't be able to tolerate the procedure.
But it was also recognised that biological sex just can't be changed which is why the law deliberately refers to gender and not sex. In a further balancing act, it was recognised that gender would need to effectively be given the status of sex for discrimination purposes.
And even then there are situations where a certificate is of no practical effect such as succession, peerage and gendered crimes.
The law does recognise that someone has to transition, it just doesn't insist that this is done physically.
Which is as it should be. Someone who goes through the gruelling process of actually trying to live their lives as a woman should be offered much more support than someone who simply states I want to be a woman therefore I am.
Discrimination law is entirely different - it's about protecting individuals, not groups, from unfair treatment which has no merit. Where discrimination is for accepted reasons, it's allowed as the principle is to do the lessor harm.
The problem with discrimination is that gender and sex are considered as major characteristics so a balancing act is very finely judged.
The standard example is that of an organisation that provides support to victims of rape. If the organisation feels that the women would suffer harm from a transwoman on the premises, it is appropriate to offer services to the transwomen off site. The greater harm is recognised to be to the vulnerable woman and the transwoman can still access support. Where it gets complicated is the stage of transitioning that the transwoman is at.
There is clearly merit that public bodies and employers should be organising their facilities to make them accessible to all which is where the EA comes in. The issue is that if no one is challenging them on that, nothing is going to be done. I think we all agree that a private accessible space is better than individual male/female/trans/accessible spaces which force people into conflicts of interest. Problem is that trans activists are shouting loudly about access to whatever space they like and failing to recognise the harm this does to every one else, including trans men and women.