that's dismal's argument. The law says you can't pay male and females differently for the same job that's the same skill and same responsibility. So a business or in this case the Soccer federation has to say one of those three is different so they can pay different.
Somebody that has followed EEOC cases would have to describe simiar cases where the two parties were catering to different market but still said they were the same.
The reason separate gender leagues exist is because of the vast difference in skill level, so vast that the distributions likely have near zero overlap.
If the court were to rule that there is no meaningful difference between the leagues, it seems they would then also have to rule that it is sexist discrimination for either league to be gender specific and they must hire players on demonstrated skill. That would result in two men's leagues, maybe with 1-2 women.
There is no way to say that without it smacking of misogyny, but dem's the facts.
I support a women's league, watch the national team more than the men, and think they should fight for and get more pay via the top players refusing to play. I just don't think they have a legal case and can't see the court siding with them on any principled grounds.