Wouldn't most group-based heuristics be useless when self-selection is involved?

Let's assume we care about strength, and that men are significantly stronger than women (I'm cutting corners for simplicity's sake).

If you're looking for people to mug in the street, and all else being equal prefer a weak victim, then you're better off targeting women than men - it's a useful heuristic.

However, if you're hiring people for a job that requires strength, people will only apply if they think they have a chance, then you should expect about the same distribution of strength among the man and women who apply - any sex-based heuristic is useless.