I don't think we need to cite sources to suggest that white collar jobs tend to be filled by people above the socioeconomic median, or the fact that the same demographic cohort overwhelmingly tends to go to college. The middle class goes to university (a) because it's a default, (b) because it's part of the middle class lifestyle, and (c) because it's perceived as necessary for a career. Only 1/3rd of those reasons are about credentials.†

Stipulating the fact that jobs are just statistically going to be filled by people who automatically got degrees, I don't think it's a stretch (or a cheap shot) to suggest that the relationship between jobs and school is tenuous.

Moreover, given the fact that white collar jobs in large companies tend to be managed conservatively, and the fact that people without degrees are outliers (because almost every applicant for any job went to college by default), some of the "credentialing effect" of a degree is actually just an observational bias.

† Note also the preponderance of college attendees who attain degrees that are almost objectively without credentialing merit, such as the liberal arts.††

†† "Without credentialing merit" being intended as an objective statement and not as an argument that people shouldn't get liberal arts degrees; I think most degrees are without credentialing merit.