I agree that demonstrated competence is what ultimately matters. The problem that I had with your example is that you said "all things being equal. . . ." That implied that the candidates were both technically competent, only one had a degree and one didn't. I understand your point that candidates that succeed despite not having a degree are probably better than a lot of people with degrees. But you are making a stronger claim than that; you're saying that discriminated groups that succeed in getting hired are probably better than others that also got in. Now, you did provide a link to a study that was true of women but I would want to see evidence specific to people with degrees versus those without. The problem with generalizing the way you seem to be is that the people you hire without a degree may not have been competing against the people you hired with degrees.
For example, suppose you have two positions to fill that are basically the same. You fill one position with person A that doesn't have a degree and you fill another position with person B that has a degree. Person A may have gotten the position because they beat people with and without degrees that were also applying to the position. The same applies to person B. On one hand, you're saying that person B will get some level of preferential treatment because he/is has a degree. But on the other hand, you're saying that person A is probably better than person B in a manner that isn't reflected in the basic competency tests that were used to hire them in the first place. However, at this point you're comparing apples to oranges because they weren't hired from the pool of candidates.
Moreover, I don't know what you mean by "better". You might say that someone that succeeds despite lacking a degree is probably more passionate than an equally hireable person that had a degree. He/she may have more job experience. He/she may have passed with an A+ from the school of hard knocks. It seems to me that the only way to quantify this and aggregate over individual differences would be to compare the long-term salaries of people with degrees versus those without. Pay may seem like a coarse measure of whether an employee is better or not (I should know because I left a job in which I was underpaid for years despite being productive) but it is at least a simple measure of how much a company actually values an employee.
Sorry, I don't have access to a study directly on degrees. If you want that, go hire some social science people to study it.
However my personal, anecdotal experience is that peer coworkers that I've had who did not have college degrees have, on average, been better than ones who did. By "peer coworker" I mean "working with me, with a job title similar to or better than mine". By "better" I mean "impressed me more". My measure of being impressed is what I thought of the quality and quantity of work that I saw them doing.
I have no idea what their salaries were like. There were some that I know were making less than coworkers with degrees, even though I thought that their work was better. Most I never had a discussion about salaries with.
That said, on the whole I would wager that discriminated against workers get a worse salary even if their productivity is equivalent or better. Why? Because salary is the result of a negotiation, one of whose inputs is what your alternate options are. People are not paid what they are worth to the company. They are paid what the company thinks it needs to pay them to keep them happy, and the difference between that and their worth is kept by the company as profit. (Companies that do not act this way soon find that they are not able to make a profit and some time later find themselves out of business...) If some employees have a hard time being paid more elsewhere, then they will often be satisfied with less from you.
This phenomena is presumably why the paper that I pointed you to measured productivity on the basis of company growth and profitability, and not on paid salary.
For example, suppose you have two positions to fill that are basically the same. You fill one position with person A that doesn't have a degree and you fill another position with person B that has a degree. Person A may have gotten the position because they beat people with and without degrees that were also applying to the position. The same applies to person B. On one hand, you're saying that person B will get some level of preferential treatment because he/is has a degree. But on the other hand, you're saying that person A is probably better than person B in a manner that isn't reflected in the basic competency tests that were used to hire them in the first place. However, at this point you're comparing apples to oranges because they weren't hired from the pool of candidates.
Moreover, I don't know what you mean by "better". You might say that someone that succeeds despite lacking a degree is probably more passionate than an equally hireable person that had a degree. He/she may have more job experience. He/she may have passed with an A+ from the school of hard knocks. It seems to me that the only way to quantify this and aggregate over individual differences would be to compare the long-term salaries of people with degrees versus those without. Pay may seem like a coarse measure of whether an employee is better or not (I should know because I left a job in which I was underpaid for years despite being productive) but it is at least a simple measure of how much a company actually values an employee.