Where to even start with this mess?
Firstly, no, access to public toilets and changing rooms is NEVER "on a case-by-case basis". It is quite literally a blanket rule, relying on individuals to do the right thing and bystanders to sound the alarm if they see someone doing the wrong thing.
This idea that trans women should be entitled to use women's toilets, which has been foisted on women without our consent, effectively upends that principle. Men who enter women's spaces when they have no business being there are, by definition, people who cannot be trusted to do the right thing. And if we are forced to accept that nice, harmless, male-born trans people who really do feel very profoundly that they identify as women should be allowed into these spaces, we lose any ability to sound the alarm. Because we are supposed to give everyone the benefit of the doubt.
Secondly, you do appear to be confirming that you think male people who have committed violent sexual offences against women should be allowed into women's changing rooms and toilets. You seem to think they have a right to say, "I am a woman" and have other people accept this as fact, which trumps any rights women might feel they have not to be in such spaces with a violent rapist.
In order to justify this position, you suggest that Isla Bryson should be allowed in women's single sex spaces for the same reason that Lily Cade and Lucy Letby are allowed in them. Lucy Letby is currently serving a whole life sentence, but even if she is ever released from prison, there is no evidence that she represents any physical threat to women whatsoever. Her victims were exclusively newborn babies in the NICU. Lily Cade has, to my knowledge, not been convicted of anything at all. Both of them are, in any case, female. Unlike Isla Bryson, who is male, and currently serving a sentence in a men's prison for committing an exclusively male crime against female victims.
Is that really the best you can do?