I understand that politics in the US is very polarised, but surely most voters don’t blindly support every single thing their party says? There have to be thousands of possible combinations of opinions in a country.

Two points:

1. Top-level sports isn’t fair. Most famous athletes are outliers in terms of height, weight, muscle mass, etc. Some, like Phelps, have genetic or developmental differences that give them a pretty significant advantage.

2. I must admit that the legal definition of ‘transwoman’ varies from country to country. In India, where I live, a person can legally change their gender without any medical intervention, and such people might have a physical advantage over cis-women. But in the vast majority of countries, they have to take hormones and / or do surgical procedures that reshape their body to be more ‘feminine’. Once they do that, they have no significant advantage over cis-women.