I’m sure we agree on much (and we know each other from Twitter of course!) but I still think the overall attitude is the main problem. As I noted, other art forms and other genres of writing (science fiction, journalism) have a different attitude toward how writing should work and consequently they get paid better.
I also think you are really downplaying the number of people who make a living from writing of some kind (screenplays, medical texts, ad copy, journalism, ghostwriting, etc.) We aren’t talking about just JK Rowling and John Green, but thousands and thousands of workers. That number grows even more when you factor in all the people who make a significant side income writing (say, 10k or more a year).
Much of this also comes to to life choices. With all due respect to Emily Gould, the fact that she couldn’t live off of a 200k advance (in a piece you linked to in your essay) is more about how she wanted to live than about how much 200k really is. The vast majority of Americans live on far far far less than that.