Thing is. Nonbinary must be allowed to mean literally anything in the way it currently is defined.
I am a man, I identity as a man. However, if I were to Identify as Nonbinary, that would need to pass - I might internally and externally be male, but if I say I don’t identify with being male - it’s sexist to deny me the right to identify that way - because identifying that way is not tied to a specific thing you do.
Your calculations don’t hold up. If you get a driver from a 25/75 pool, you are 25 or 75 percent likely to get that gender as your driver, no matter your own gender. So this 0.5 times is not needed.