Someone please tell me if they find the quoted argument intelligible though.

It would seem he's saying that you cannot use the m/f ratio in this population to determine whether or not anti-discriminatory practices are effective or ineffective. Since the hiring process itself does not yield a randomly sampled population (you cannot discount biases, applicant self-selection, etc.) the likelihood of drawing erroneous conclusions from this population makes the effort of drawing statistical inferences from it worthless.

More simply, he's saying you can't conclude that the gender and race gaps in this population come from any place other than different parts of the hiring and recruiting processes. You also cannot say that changes made to the hiring and recruiting processes will yield lower standards and decreasing false negative rates based on the current population distributions.

The statement both agrees with some of your original points while disagreeing with others. Trying to find the perfect race and gender ratios by trying to determine whether certain races or genders are innately more suited for certain roles is a meaningless pursuit.