If they were maximizing talent, they'd choose those most fitted for the role. However, those things are skewed for a variety of factors (some of them genetic) towards the very groups you are accusing of advantage. If you truly want to get past the "advantages don't exist" perspective, you'll have to actually come to terms with the fact that genetic advantages exist (with the important caveat that there is more inter-race disparity than intra-race disparity). If you are willing to "get it", we can begin to talk about ways to balance a society that can deal with these disparities in a way that isn't overtly racist.
I would think this would include not trying to balance membership in specific types of labor with those for whom it is not as well suited. As such, we would expect the numbers in any given labor field to reflect a sampling of the groups of people for whom their talents and interests match up well with the labor division.