None of the studies I've seen have even considered whether a privileged background does translate to higher than average merit. And why wouldn't it? We already know household income is correlated with IQ, and growing up having access to better schools, better extracurriculars, less influence from crime, etc is likely, or at least possibly going to build a more competent child.
This field is hopelessly biased. These soft "scientists" start with the premise, that we are all equally competent and set out to prove that cultural factors simply get in the way of perception of merit. The irony is that these same people harp about workplace culture, with claims that "good" [PC] culture has positive effect on business outcomes - doesn't it follow that different home cultures will similarly effect adult outcomes? Why won't anyone with academic clout admit that the culture of your childhood effects how much you're likely to learn, how disciplined you're likely to be and, ultimately, how well you're going to function in a professional environment?
It's a conflation between equality of opportunity and equality of outcome. Frankly, is bad for business and bad for society.