> And isn't that just a tautology?

I don't think what I said is tautological, so let me rephrase.

I think it's a mistake to leave a field early solely because there are fewer jobs than people with the relevant degree. Not all jobs are created equal, and not all degree-holders are equally competitive for all jobs. Some positions have a hiring bar far above having a qualifying degree. It also helps to realize that programs graduate C and D students all the time.

So it can both be true that there aren't enough jobs for everyone with the degree, and also that the market is not saturated with qualified candidates for particular jobs.

> Isn't the point that we might think that getting a terminal degree would qualify a person for some kind of job in their field?

As you climb the ladder, competition gets fiercer. At the terminal-degree level, having the degree is the baseline expectation. Not having it may be enough to disqualify you, but having it is not enough to make you competitive, because your peers also have terminal degrees. A terminal degree may qualify you in the credentialing sense, but it does not guarantee that you meet the hiring bar for a particular position, or that there is sufficient demand for your specialization at the wages, locations, and conditions you want.