From what I've heard, writer's income looks like a power-law distribution — you get a few lottery winners like Rowling, but most authors, even most of the ones you've heard of, earn so little from the writing that it's a second job.

Even ignoring AI, the maximum possible market for writers is also quite small: If every single person buys a new book every week, even if this money is evenly distributed so that every author gets £12,000 per year (fantastic if you're living where The No. 1 Ladies' Detective Agency is set, not so much when you're living where the series author is based), that's a maximum of about 34,667 authors worldwide, which I think is about the number of agricultural workers in just famously small and not-agricultural Singapore[0].

Personally I am of the opinion that arts should be funded mainly by government grants, though not entirely from them as free markets do at least help align production with demand.

[0] take with a pinch of salt, the stats (page 72) look like they're rounded to 0.1% and I've not read the details: https://hdr.undp.org/system/files/documents/2018humandevelop...