And even now we have spoken word and slam poets that sell out clubs & college gigs, and make ends meet on that. They are profound exceptions. And, also, Shakespeare's profits would be almost entirely due to his plays.
Yet, professional comedians make good money. The best are multimillionaires.
The developments the author points out aren't exactly new or exclusive to this century. You can trace them back to the Industrial Revolution. The 19th century English novelists I read seemed to populate their novels with characters who did nothing but drink tea, read books, make smart quips and over the summer, play a game or two of cricket (hallmarks of the quintessential Victorian gentleman, I was told). You had people who read as a hobby, and people who 'read' (and write about their reading) as a vocation (Matthew Arnold comes to mind, as do an unending list of independent lexicographers, researchers, and scientists).
And extreme success isn't stable. You can fall from the top into nowhere-land at any time.
It's ironic that many engineers believe the arts are a soft career option.