The legal aspect is crystal clear. It's blatantly illegal to ban entry based on gender with very few exceptions (such as toilets or domestic violence shelters). I expect the court will be angry that it even went to court at all.
The purpose of a judge is to settle disagreements. When both sides of a court case agree with the facts, then there is nothing for the judge to do, and it should not go to court at all. It should be settled out of court.
It's likely to be a really short case "did you have a policy to ban men?" "yes". "case closed; moving on to damages"... but the thing is, even though the meat of the case will be over almost instantly... there will still be weeks of work done in the lead up to the case, by both legal teams, but the court, by the judge, preparing the jury if it's a jury trial, etc (imagine how angry your boss would be if they had to give you paid time off work, delaying project schedules, over this case).
If you want to make a political statement, the court room is not the place to be doing that. At a minimum I'd expect the court to force one side to pay all of the legal fees of the other side, and on top of that the court might charge them with abuse of the court process which could result in punitive fines and also discipline against the lawyers involved (they could even be banned from practicing their craft). Judges don't have a sense of humour and they are not interested in political debates.
I'm sorry but the fediverse is full of instances that block other instances. Blocking an instance is not bad behaviour on the fediverse.
If you don't like Threads, don't use it (I'm not using it), and if you want to use an instance that blocks Threads... you're welcome to do that.
But what I don't get is the idea that threads is somehow trying to kill the fediverse. All of the evidence is to the contrary. Meta wants to exist in a federated world. That doesn't mean they will allow access to all content on their corner of the fediverse, nobody wants that. All instances block some other instances and threads has every right to make their own choice about who to block.