I think you're mostly right. We value specific output, not the time that went into it, and so we're prepared to pay nothing for the bulk of what is created, but a lot for a tiny little proportion.
With the caveat that you can make a lot of this pay reasonably well if you're willing to see your hobby as a craft where there is a trade off between quality and effort as opposed to art. E.g. I can write reasonably well, better in my native Norwegian than in English, but I realize that to reach a level that would let me write a novel that a "real" publisher would be prepared to publish, for example, would take a massive amount of effort with no guarantee of ever achieving it, and publishing something in Norwegian would be less likely to earn me anything than getting published in English.
But if I'm prepared to churn out quarter-novel sized English-language serialized novellas for Kindle, I'd have a decent shot at making a living at it (though not anywhere near my current salary), I think, based on my experience and the assumption that I'd need to basically churn out 10k words every 1-2 weeks at least. I believe that speed would be sustainable for me, but at a quality level that is at best craft rather than art, and I don't think it'd be sufficiently enjoyable to be worth it.
But some of the most prolific fiction writers do sustain that for a long time, and some manage to gain success that way. E.g. the original "Morgan Kane" series of 83 novels is one of the most successful Norwegian book series of all time, selling a combined ~20 million, despite only about half the books even having been made available in print in English. Most of them were written in about a month each, and while their aggregate number of copies sold over time are high for a Norwegian author, he achieved that through long term notoriety built up over more than a decade of having new novels published every 1-2 months (he wrote other series as well), rather than overnight success - the number of copies sold per book was not that high, and when he "came out of retirement" to write six more books 20-30 years ago, despite his fame, people ridiculed his publisher for doing a 100k first print run for the first of the new books, as 100k is a lot for a western book in a market of 5m people and he was not seen as someone writing high quality best sellers but as someone churning out decent, fun cheap paperbacks that'd take 10+ years to reach those volumes. They were wrong, but they were probably wrong largely due to lots of pent up demand from fans of his back catalog combined with the fact he spent 6 months to a year per novel in the new series rather than rush them out to hit a 1 month deadline.
Incidentally the author of the Morgan Kane series got rich from it, but was also least once, before his latest series, denied entry to the Norwegian Authors Association because one of the criteria was that you needed to have published three novels of sufficient literary quality. The admission committee all agreed he'd done so, but they initially at least couldn't agree on a set of the same three books. I believe they decided in the end it was a sufficiently unique case that he was granted entry anyway.