I believe Merrymouse's view is that there have been international judgements that the UK has to have a proper mechanism to formally recognise a "sex change". And that the GRC provides that mechanism.
Then in the absence of that, we would be back to the ad hoc situation that was ruled against.
I believe where we differ is that I think the Goodwin court's issue was that we didn't have a proper mechanism. There was an ad hoc mess. The judgment's basis, as I understand it, was that people could be left in a sort of weird limbo, half recognised as having changing sex, but not acquiring the full rights of that sex. They wanted the fuzzy legal status formalised.
Many seem to interpret the judgment as meaning that we had to handle "sex changes". But I don't think that's the case.
I'm obviously not a lawyer, but I believe that the issue can equally be resolved by being clear that there is no mechanism to have a "sex change" recognised by the government. Removing the mess that Goodwin was complaining about.
That could have been done at the time, but clearly there was no political will to do that - people had not yet fully comprehended what a mess the partial recognition was doing, let alone what a mess the full mechanism would cause.
We've now had subsequent UK judgments that legally without a GRC you haven't changed sex, so it seems the ad hoc mess has been cleaned up. We now only have that one mechanism, and it can be revoked.