They won't be taking their balls and going home out of pique, they'll be doing it because they have to go to work.
Every hour an artist has to spend at a day job is an hour they can't spend creating. It's an hour they can't spend practicing. It's an hour they can't spend raising awareness of their work.
This is true but as a sort of counterpoint I think that sometimes once an artist gets well established they lose some of their connection to the normal world.
For example a lot of rock music comes from anger and frustration of having to work a shitty job, behave in a prescribed way and having little money.
As soon as you have released a few albums and have free reign to fill your nose with coke , cover yourself in tattoos and can afford to live wherever you like you may lose some of initial meaning behind the art and start to become pretentious and contrived.
Your premise doesn't seem terribly strong for a few reasons.
1) Artists have memories. When I was much younger, I worked as a telemarketer. It was probably the worst job I ever held in my life. It was soul-crushing. Even though I am now a reasonably successful software engineer, I still remember how difficult it was to go to work knowing that unless I was lucky, I was going to be rejected all day long. Even though I've been with my partner for more than a decade, I remember how chaotic, foolish, and frustrating the dating scene was. Anyone with a few years under their belt knows that a bad memory can jump out at you and make you feel exactly the way you did when it happened.
2) An artists music evolves over time. Look at the Beatles. "With the Beatles" is an astonishingly different album from "Abbey Road." Just because you start out as one thing doesn't mean you have to be that thing for the rest of your career.
3) Look at artists like Johnny Cash, Bruce Springsteen, John Mellencamp, and even Billy Joel to some extent. No matter what your opinion of their music is, it's hard to argue that they are not iconic representations of the "everyman" in music. Most of their output was produced while they were some of the highest paid performers in the world. Even a guy like Jay-Z hasn't been poor or street for a very long time, but if he puts out another record, you can be damned sure that there will be millions of people who buy it because he knows how to write songs that relate to the kind of person he used to be.
Don't put too much stock in the idea that you have to be street level to write good music.
I think you have a point but it's totally irrelevant. You're basically sayng that good artists should stay poor and work a day job so they can keep in touch with their roots and make good music. Well, maybe they should, maybe not but there's no connection to copyright here at all.
Every hour an artist has to spend at a day job is an hour they can't spend creating. It's an hour they can't spend practicing. It's an hour they can't spend raising awareness of their work.