Admission at Georgia Tech has spoken on this online. Per their analysis, they can definitely differentiate the top 30% of applicants from the rest and it makes a difference in performance. Within the 30% they have found no differentiator that significantly impacts their academic performance.

So they have a full 30% of their applicants qualified to be there but they have to narrow it to 1%. Whatever method they choose must have the appearance of meritocracy, abide by laws and regulations, be resistant to corruption, achieve goals other than academic performance such as culture, volunteering, and sports, and so on.

I think the same must be true for companies. At some point in the elimination process everyone is technically qualified, so they might as well hire someone "because we like his face". But that's demoralizing and corrupt so they invent some criteria that on its face seems useful, even though it's truly not.