For me the more useful distinction has been: how close are you to the customer? If you never interact with them, not even indirectly through a team manager directly interacting with them, you're probably working more in a "staff" role under this categorization regardless of who is actually using the thing you're building. Admittedly this has problems -- you have to figure out who the customer is, for one, but it's legitimate for them to be either internal or external, paying or not. And for many companies (perhaps especially "tech companies" and tech startups) it often ends up being both via dogfeeding. I think the presence/absence of the customer in short feedback loops alongside those actually making and maintaining things dominates the distinction of whether it's staff or line. Focusing this way does help avoid the sometimes difficult distinctions of what makes a company tech or non-tech and how reasonable people can disagree over some particular example, whether what you're doing is really important to the company's overall success, or whether something is a profit center or cost center (I find it more useful to think first about whether an individual employee is an Asset/Profit or Cost, and note that being a cost isn't necessarily bad but also types can change over time).
Still, even customer proximity is not always a useful distinction, and certainly doesn't have to be a static one. I wonder if this industry resists distinctions among people or groups like these due to something at the root of the hacker culture that created it, like a realization/commitment to the idea that the only really worthwhile distinction is the bit.
I'm not sure I buy the dark matter idea. In the US there are only on the order of a few million software developers, you don't have to go very far down a list of FAANG/FAANG-like high paying tech companies to reach on the order of a few hundred thousand US-employed programmers at those firms (~10% of the market, already exceeding ordinary matter's 5% of the universe). Decide on a consistent definition of tech company in general and add in all of the programmers from them and it wouldn't surprise me at all if tech company employees actually exceeded non-tech, though I can see it being the other way too, just not being "vast majority".
As for stories from roles at non-tech places, most are probably told orally (especially to fellow employees at larger companies as cautionary tales of the crazy messes out there that make their own current insanity look pretty sane) but also remember that at any given time like half of the professional market has been in it for less than 5 years (how many of them got into tech-company vs non-tech-company roles?). And remember you may have read stories from them but not realized it because the actual work regardless of line/staff or tech/non-tech company distinction itself for programmers can be so similar, so it's not always clear whether some story on e.g. The Daily WTF is from which (though sometimes it is or you can guess).