That you simply invert my number argument sounds correct at first glance, but is a misuse of statistics, as it completely leaves out the fact that 1 trans in a female facility does not make 1 woman feel uncomfortable, but eventually a large number in there, depending on the type of facility. Just think about a sex segregated sauna with a dozen women in there, and a trans entering (This is an example, for illustration purposes. Because of lack of knowledge of those things I have no idea whether in the US or elsewhere that's possible now or in the future).

I discussed that in my post. The number of cis women made to feel uncomfortable is likely larger than the number of trans women. But it's not "all cis women," because there just aren't that many trans women out there.

Though I think you're making a statistical error. If you have a thousand such saunas, only one or two of them will have a trans woman in them. You've got more cis women than trans women in the one or two saunas where they do mix (let's assume 0.2%). But you also have multiple cis women in the saunas that don't have trans women. The number of cis women who are interacting with the trans women is still only about the same proportion as the number of trans women in the population. They're interacting in "clumps," so within each sauna room you have a 12:1 ratio of cis women to trans women - but because the "clumps" are still small relative to the overall population, the proportion of cis women interacting with a trans woman doesn't really change. It's still only about 0.2%.

And of course, if you force the trans women off to the mens' locker room, that means the trans men are coming to the ladies locker room. So it's not like the cis women are now free from discomfort. Roughly the same number of women who would have encountered the trans woman are now encountering a trans man. He won't necessarily have a penis (though he might!), but he's going to otherwise have a male appearance.

Balancing the interests involved doesn't dictate a single right answer. Again, the policy-makers have a choice - one policy (possibly) makes more people uncomfortable but materially reduces the incidence of violent assault, and the reverse policy has the reverse outcome. Which is the "right" policy? Depends on how you balance people feeling uncomfortable with people getting the tar beaten out of them, adjusted for the relative population sizes. But the population size for cis women isn't all cis women, because (again) there are so few trans women that most cis women just aren't going to have that interaction.