This was brought up with Michelle Dumaresq, a pro mountain biker (mtf).
They first argued her strength, but later the figures came out that at about 2 years there was little difference. They also pointed out her physique, but if you look at her mom, she is actually somewhat similar.
Opponents then went after how she was raised. As a boy she was encouraged to ride bikes and be rough and tumble so she had an advantage they claim. This may be somewhat true. You were raised to swing like a guy, and play like a guy, and expected to perform as one, whereas girls are often not.
The problem I see with this whole argument, is that it is mostly B.S.
Yes, you may have been trained under different circumstances, so what happens when a genetic girl is raised under those same conditions? Men who are prepped for a specific sport do better than those who don't, the same would apply to women. So who do you blame for a girl, or a guy for that matter, not having started training at a younger age.
If you decide at age 30 to train and enter a triathlon and lose, do you blame the person who trained their whole life for it and beats you? You had better training, whether guy or girl, plain and simple. You may have had an easier time obtaining that training, but there is nothing to stop a girl from training for a particular sport from a young age. There are many these days who are and now we are seeing more and more women who can compete with men on the playing field.
I know a few women who can ride a bicycle as well as the guys do. If a girl is raised to be pretty and petite and do nothing but look pretty, of course she will not be as good at sports as the girl who goes out and played football with the boys.
