The standard in many sports is... documented use of testosterone blockers for 2 consecutive years, and a testosterone test showing T levels lower than some number that is clearly within the natural ranges.

If you dig into the sports involved, they generally all have run studies. There is a point where any advantage of being born male becomes negligible. It's not (just) about identifying as the destination gender. It's about showing zero or limited advantage in the league.

Ironically, it looks like the bigger issue is with trans men, who tend to somewhat outperform cis men in certain base tests of strength despite having compatible testosterone levels.

As for breasts in swimming. You understand that it is not against the rules in competitive swimming for a cis woman to get a breast reduction, right? If Cis women have no requirements or limitations on that, why should trans women?

What if I didn’t want to subject my body to hormones just to be considered the gender I feel like I already am? That should be my choice.

Then don't compete in the destination gender's circuit? Turning gendered sports into hormone-matched gendered sports is an entirely reasonable compromise because you're defending the competitive integrity without being bigoted against a person.

A trans individual is not welcome in their birth gender sport because they resemble (hormonally) the other gender. It seems contrived to defend exclusionary behavior on "what if I want to do what would include me in the other category".