You're assuming that people arguing for bans on trans athletes are making good faith arguments about competition in sports. You shouldn't.

Here in the US a significant part of antipathy towards trans people is the deeply held belief that being trans in public is a kind of sex abuse to the public. If you listen to what much of the debate has turned into here, it has little to do with competition, and far more with the obsession over what genitals people have in locker rooms and bathrooms.

At the end of the day the number of trans athletes is so vanishingly small it's not worth caring about the impacts on competition, when the debate itself is another framing of the conservative desire to make being trans illegal.