If cis women are generally better than cis men at freediving, I'd argue that actually bolsters my case that cis women are not inherently inferior in sports. I wonder how much of this narrative is based in sexism rather than science. After all, within my lifetime women were barred from competing in (standard) marathons and told that distance running would dislodge the uterus or similar nonsense.

The example you give of the trans equestrian is ridiculous and infuriating. The horse is the athlete here, not the human, so why should it matter what kind of body the rider has?