Everyone is subject to it. If you are an XY athlete, you have to go to the XY division. It doesn't matter whether you are gay, straight, trans, or furry. The rule is the same for everyone.
You're trying very hard to turn this into a debate over testing protocols. There is no need. People know their child's birth gender. You can just ask.
And, for the very few people who would lie about it, you can kick them out, same as we kick out people who lie about their child's age. We don't have some hugely complex system for enforcing age limits by measuring telemeres. We just kick out the cheaters if and when we find them.
So now you are back to ignore the unicorns (the cheater...they can just hide among the horses), the zonkies (the nonbinary who chose not to disclose a gender), and now the dragons (the genetically and chemically unusual), but death to the pegasi. It's easy to tell them apart anyways....they are the ones flying up there. Nice. And you wonder why you get accused of bias.
What's worse "if and when we find them" sounds an awful like the Utah witchhunt. Nice you are so prepared to subject the innocent cis girl to that.
Gotta say, I keep wondering when the end of the pit of horribles finally hits with you, but so far there doesn't seem to be a bottom. There must be one. I just keep listening for the "thud" and get surprised when I don't hear it.