Yes, trans women are women. Agreed.
The challenge is that trans women are women who used to have comparatively vast quantities of testosterone in their bodies, giving them dramatically higher bone density along with all of the other side effects of testosterone on the body.
When they transition fully, the estrogen has a side-effect of preserving the bone density they had previously. Specifically, this gives them a massive advantage in combat sports like MMA. I won't get into the other musculoskeletal aspects that happen.
It's a vexing problem, because I don't like the idea of trans women not being treated like women. It sucks to think about that. It also sucks for non-trans women who are getting their skulls fractured in fights.
The reality is that fans of non trans female athletes aren't going to accept this. When a tiny percentage of the population is trans, and suddenly trans women start winning at the highest levels of female sports at an insanely disproportionate amount, it clearly indicates that being trans provides a massive advantage in female sports. I haven't found any cases of trans men dominating in male sports.
I'm pro trans rights, and also know that my view on this is deeply unpopular in the trans community. I'm not sure what the answer is for this. Sometimes, reality doesn't mesh with our ideals.