Lots of research happens at government agencies, non-profits, museums, for-profit companies and international projects (e.g. ITER). As long as a grad student doesn’t insist on making faculty, they’re not necessarily constrained to a zero-sum field.
But it follows the same logic even if you bring in your point about other outlets. Those obey the same rules too. Unless government expands, museums grow, or some tech company has a need, there's also a finite set of jobs being competed for by an increasing population.
Some fields have it better. In biotech, computer science, engineering, etc. at least those are growing, viable, and profitable fields (and respected). In other fields, not so much. Not only do you not find a job easily, you get looked down upon for leaving the "pure" path, when in fact most people eventually have to face that future anyway.
At the end of the day, unemployment numbers for holders of PhDs [1] are starkly different from those of the general population.
And then there's the "just learn to code" cliche.
And I mean a PhD working at a McDonalds still counts as employed, right?
But this is a life of hopping from low-paid job (supply and demand) to low-paid job every 2-3 years trying to build the connections and reputation to eventually hop back into academe. The alternative is getting out of "research" and becoming a normal employee, where noone even cares about your PhD or publications.
So, where is the competitive advantage? It is in the PhD itself (first), the methods that have been used and the skills acquired (second), maybe the volume of publications and the number of citations (third). Talking about research and papers is like trying to convince a potential partner that you are interesting and charming and lovable, when you are extremely good looking. Use what you have, not some idea on what other people should appreciate in you.
This assertion doesn't play out in the real world. A graduate student does not have exclusive access to these non-academic positions, nor is the skillset developed in the academic niche world applicable in non-academic environments.
In fact, the realization that graduates with an academic background underperform in non-academic settings is widely known, not to mention the negative impact that some soft-skill traits developed in academic environments have on their employability (for example, the false sense of entitlement).
Imagine a corporate lab: there's trained researchers, as well as technical/lab staff (preferably with a solid apprenticeship). Now you have a 30 year old technician who worked in the field for >10years and in parallel did some community college BSc, so has at least some calculus, very basic mechanics and whatever domain-specific-science background there is. Both this one and a MIT grad apply for a technical, managerial position managing technical aspects of the lab/department.
I bet, today, the MIT grad is not too far behind, even if he has no idea of the social dynamics with all the people, skills in procuring stuff or even properly doing labwork. Great, not?