For starters, it's essentially claiming that all young girls consistently suffer from the effects of
growth hormone deficiency, which has a constellation of symptoms that would be very easy to spot.
The International Olympic Committee has specifically had to
restrict the entry of hyperandrogenic women, precisely because their athletic performance tends to be well above the female norm, due to their levels of male sex hormones. Conversely, transsexual men and women are
allowed to compete in their respective categories, because their altered hormone regimens induce performance within the norm for their target sex.
You are claiming that cultural differences in gender perception result in differences in childhood exercise that systematically reduce the performance of ALL women. Therefore, yes, I'm afraid that a single counter-example deflates this argument.
Besides, the attitude that cultural gender roles will systematically limit achievement in ALL cases is as dehumanizing as the idea that biological sex will do so. It dismisses variations in life experience and personal choice just as the latter dismisses variation in natural talent. Even with cultural differences between gender- which I believe are virtually irrelevant to something like bodybuilding, unless severe malnutrition was a factor- there are going to be a certain number of women where optimal environmental variations coincide with optimal genetic variations to allow for maximum theoretical performance. These are the women you would see at the top of their game,
and they still can't match the top men.
Your reaction, in essence, is to call them lazy or their parents negligent, and that is uncalled for.