Tandora, you are completely misunderstanding the role of the Supreme Court here.
It was not their job to consider the meaning of things like gender and "transness" or even to consider what might be at stake for trans people.
Their job was merely to apply the law. And as you say, they are "respected legal minds", and there is absolutely no indication that they interpreted the law incorrectly.
The law in question is the Equality Act. If you actually read the Equality Act, its purpose is clear. And the clue is in the title. It is designed to ensure equality between different groups of people. Equality. Not special privileges for trans people at the expense of women.
Now I know that trans activists like to play the oppression Olympics, creating a hierarchy of oppressed people with trans people at the top, and telling women that they need to "be kind" to these heterosexual white male "women" because they're so much more vulnerable and marginalised than we are. (Even the ones who happen to be convicted sex offenders.)
But the law does not actually work like that.
The law does not establish a pecking order in which trans people are more important than women.
The law establishes principles designed to ensure that everyone is treated with equity and fairness, and that where having a protected characteristic gives rise to a certain need, efforts should be made to meet that need. (For example, female people need rights relating to pregnancy and maternity, whereas male people do not.)
You are making the fundamental mistake of assuming that this is a bad legal decision because the Supreme Court judges failed to consider the impact on trans people of upholding the law and saying they shouldn't be in single sex spaces for members of the opposite sex.
Speaking as a lawyer, it's quite extraordinary to see a non lawyer effectively claiming that the Supreme Court reached the wrong decision because they did not consider the effect of the law on trans people and decide to override it. Even if a law is bad, it is not the role of judges to override it. The most they can do is deliver a judgment which says, "This is the law, it has a negative impact on trans people, if this is not parliament's intention then perhaps they should consider amending it."
The other thing which is quite extraordinary about your point of view is that you appear to think that the impact on women of allowing trans people to use single sex spaces for members of the opposite sex is irrelevant.
You are literally complaining that the Supreme Court did not give sufficient consideration to the impact of its judgment for trans people, and that instead it gave consideration to women.
When looking at the protected characteristic of "sex", the Supreme Court judges asked themselves the following questions.
What is the normal meaning of these words?
Which group of people was parliament intending to protect when it created this protected characteristic, and why?
What would be the impact on that group of people if we take an expansive approach to the meaning of these words, so that members of the opposite biological sex can be included?
The Supreme Court judges came to the conclusion that parliament could not possibly have intended "female" to include members of the male sex, because the impact of that would be to undermine the very protection for female people that they were attempting to enshrine in law.
As the judgment so eloquently says in relation to single sex spaces, if it is reasonable for a woman to object to the presence of the opposite sex, the reasonableness of that objection cannot possibly be based on whether a member of the opposite sex has a gender recognition certificate or not. In other words, the presence of someone like Karen White or Beth Upton in a women only space is going to have the same detrimental impact on women whether they have a piece of paper saying they are a woman or not.
It absolutely beggars belief that in one breath you describe yourself as a feminist, and in the next breath you are complaining that the Supreme Court did not consider the impact on male people of denying them access to female only spaces, and only considered the impact on female people of allowing male people into female only spaces.
It is not the job of the Supreme Court, or even parliament, to enforce feminist principles.
But it is the job of feminists to consider how things impact the female sex, and to fight for things which have a positive impact for the female sex, and against things which have a negative impact for the female sex.
If you have read the Supreme Court judgment and you disagree with it, you are not a feminist.
And if you have not read it, your opinion on it is worthless.