There was a Supreme Court case about this very thing regarding UC Davis back in the 70s. At the time they had a numbered quota for minority students that they had to hit (much like United has claimed they will do). The data showed that the average GPA of the quota meeting students was sub 3.0 while students with significantly higher GPAs, who just happened to be white, were getting rejected because all the non-quota spots had been filled. I can’t remember the actual numbers; I did a report on affirmative action way back in college, but you can pretty easily look it up. There are other cases as well along similar lines, a more modern one had to do with UT-Austin, but I can’t remember the specifics of that anymore.

The theme of quotas lowering the quality of an applicant pool is legitimate though.

The actual way to increase minority representation is to encourage whatever activity/job/etc... from a young age. School out reach programs are massively needed for this and then you actually build a quality pool to pull from. The problem is, such a grass roots effort can take decades to show results. Much easier for politicians, business leaders, and universities to set quotas and just increase the raw numbers, quality of the applicants be damned, and then pat themselves on the back about how tolerant and woke they are.