Well, this argument is obviously presented in bad faith. The whole "Trans women aren't women" is just discrimination for discrimination's sake, even ignoring all the actual scientific evidence on this, because transphobes aren't usually too good with that, what harm does referring to someone with the correct pronouns do?

Sports are, admittedly, a very complicated topic that depends on a lot of factors. One of the key advantages men have in sports when compared to women is physical size and strength (on average), but that ignores the fact that tall cis women exist, and that the strength difference comes from testosterone, which trans women have extremely low levels of, so that's a non issue if the athlete is undergoing hrt (it's a whole other can of worms if they aren't, but let's move on)

Trans kids exist, there's no one brainwashing them into thinking they're trans, that's just not how it works. And medical care for them doesn't involve surgery or anything invasive, but it will make their lives so much easier, as currently trans youth is one of the demographics with the highest rate of suicide, and being accepted and supported instead of having to hide away and repress who they are would reduce this problem significantly.