As someone who wears trousers almost all the time, I can't get really upset about this.
Yes, they made the male uniform the "neutral" version. True.
But the English language does that all the time. Job descriptions - all masculine. According to Terry Pratchett, any female shepherd with any self esteem calls herself that - not shepherdess.
Only job where I've seen the feminine option regularly used was "actress".
And you know what? It works. The masculine version may not have been neutral in the beginning, but the more people use it like that, it does become so. (And let me tell you, it works better than in German, where only the most committed people make sure to always use the feminine form, too, when talking about a group. Most default to the very definitively masculine form in the plural.)
When people started to talk about "hatred of femininity" or whatever they call it, I listened. It seemed to make sense. But now I see that those same people deny the very obvious and simple fact that men oppress women because of our biological sex. Because of reproduction. Not because of skirts.
In the end, how much does not being allowed to wear skirts harm girls in a real, material way?
It is one option less, sure, but ... let's just say, it is not a hill to die on, for me.
Girls not being allowed to wear skirts is better than them not being allowed to wear trousers AND being bullied about their alleged lack of "decency" while wearing the same skirts they are forced to wear.