The science here is a bit more roundabout. The women’s leagues appears to have been started in the first place (based on some of the other posters here) because males have more success at the highest levels than females. Everyone acknowledges that this gap shouldn’t exist, yet we still have it. So it’s not a scientific basis justifying the segregation, it’s that science can’t explain the outcomes, so the segregation was established to try and make the outcomes more equitable.
Another poster asked whether trans women somehow need to “prove” that they’re oppressed to the same extent. And, ultimately, that might be what’s required, as absurd as it sounds. Because I think we legitimately don’t know whether this male advantage maps to all males, or just those born male.
Maybe, once we establish some data from more trans women competing at the highest levels, we’ll be able to answer that. For now, they made a decision which basically turns the women’s leagues into cis-women’s leagues.