It looks to me like the study cited previously addresses your point by asking students whether or not they'd like to gave an academic position:
"When asked to ignore actual job availability and rate a range of careers, only about 50 percent gave an academic research career the highest rating; more than 40 percent gave top marks to research jobs in the private sector, while about 30 percent thought working for a startup would be pretty great."
I don't think that covers it. When people are forced down a path, they find ways to rationalize why it's better than the alternatives. That is, you can't just ask someone to ignore job availability and expect that their view of the job actually does ignore job availability. Their view of the job probably has it already baked in. Self-evaluating a cognitive bias is hard.
Although it’s unknown how these preferences translate into the careers people actually pursue, the implication is that only about half of doctoral science students are really gunning for academic positions. NSF data support this. In 2010, about 50 percent of new science Ph.D.s went on to do postdoctoral research at a university—the contract job long considered a necessary step for landing a professorship.
Grad students who are looking for jobs know ahead of time how competitive it is to get academic positions. We can do the math. When it was time for me and the others in my group to start thinking about what to do next, we looked at the Computer Research Association numbers: 1500 new CS PhDs were made the prior year, and there were 100 academic CS positions open in the country. So our competition was roughly 1500 people plus more experienced people switching from industry to academia, or tenured professors changing universities. (In which case it's possible their old position may not be filled.)
We also had spent many years observing the professor hiring process at two schools, and knew what it took to be competitive.
I imagine some new PhDs don't try for academic jobs because they've ruled it out as unrealistic. They may not be trying for an academic job, but for some of them, they are still on Plan B.
My point: even though 50% of new science PhDs don't go for academic positions, it's still a problem for them that there are so few academic positions.
I'm pleased to read an essay which distinguishes between technical and liberal arts PhDs, and I agree with the things that are not related to this point. But this point is a big one, and I'm afraid the author is misinterpreting the results of the cited studies.