Yeah, testosterone levels vary, but a male human is born male, regardless of testosterone levels, and the same goes for women. Men, however, as a whole (with exceptions in either extreme) have more physical advantages over women (muscle mass, lung capacity, explosiveness, etc.), and it's unfair to try to compare men to women simply because they say they're women, and vice versa.
If someone wants to make a unisex sports league for any sport, that's perfectly fine. Men, women, and people who call themselves whatever they want can compete in such a league. However, it's unfair for a "transgender woman," which is simply a man who either messes with his natural biology or just wants people to take it at his word, to compete with women, as in women born women, and it's wrong. And of course, the same goes for women cosplaying as men.
