the traditional answer to this is something along the lines of the idea that writing is not fungible; that is, just because we have a lot of writing, doesn't mean we have enough good writing. What good writing is varies, but clearly there is some level of quality that exists, at least at the bottom end (its not hard to find people to agree on whether a work is objectively bad writing)

unfortunately, precisely defining good writing is difficult, much like good coding. And as such, whether there is enough good writing, or "how much better good writing is to bad writing", or "what the effects of good writing are on the individual or society" are questions that we arent remotely prepared to answer. I imagine many people advocating for support for writers believe on some level both that good writing has very positive effects for the readers and society, and that there also isn't enough of it, or at least that its drowned out by perverse incentives and mountains of bad writing