I'm disappointed - this article is very short sighted. Everything in it is about recording and making money from concerts and stuff. It's all modern. When was the time of the middle class musician? What was the distribution of musicians as a primary job vs all jobs?
Throughout history it seems that there has always been an imbalance of musicians that make good money and those that don't. It seems that most musicians did it for free as part of a community/spiritual ceremony, or did it as a part time thing.
The modern issues are related to the technological advancements. The true cause of issue the article talks about is right in the beginning of it - music has never been easier to make and record. Supply and demand?