It's exactly an argument from tradition because the purpose has been laid bare "some half of people have innate biological advantages", and exactly the subject is "how do we protect those without those advantages from competing with those who have them, for the sake of fairness?"
Your argument is literally, '"sex" is what we did, sex is what we should do' insofar as you stand with Metaphor.
that's like saying it's only an argument based on 'tradition' that we use gasoline to fuel combustion engines, or only an argument from tradition that we use electricity to power devices which use electricity.
there's a fundamental reality-based purpose for the behavior in the first place, and none of the factors that go into that purpose have changed just because some folks such as yourself seem hell bent on arguing that a statistically insignificant (to the point of it being functionally non-existent) aberration constitutes an argument against the existence of the whole.