we presume that observations are not caused by biological differences without concrete evidence of those differences. The corollary to that is that disparities in outcome are prima facie evidence of disparities in opportunity.
Is it? I think it just means you need evidence of biological differences (or lack thereof) from things other than disparities in outcome - from outside the circle.
If I say "Women aren't as fast at sprinting as men, and it's biological, as evidenced by the fact women aren't as fast as sprinting as men" I agree that's a circular argument.
But if I say "Women aren't as fast at sprinting as men, and it's biological, as evidenced by these studies of testosterone levels and their effects" that's a non-circular argument.
I agree with the last part. But here OP said "we presume X is not a factor", and then goes on to conclude X is not a factor.
OP requires evidence for biological differences, but requires no such thing for the discrimination theory.
Throwing around "epistomological presumption", "corollary"' and "prima facie" does not make this a scientific argument.
In reality there is plenty of evidence for biological gender differences (and for discrimination). Pinker's "Blank Slate" is a good start if you have time to read 600 pages.
This is a textbook circular argument.