Mainstream recording artists (pop, country, R&B, rock, etc.) represent the vast majority of industry revenues. My argument is that middle class musicians have effectively never existed in this space. Just like middle class professional basketball players effectively don't exist. You either win big or do something else.
There's no doubt that there are some middle class and higher earners. It seems that most are part time, don't make much and face higher unemployment than many other sectors. Sector growth is alaso very slow. There's a reason that most people's parents don't push them to pursue music careers unless it's as a teacher or if they're exceptional. Same thing for sports - you can make decent money as a college coach or gym teacher, but the proportion of people who play sports that go on to do anything professionally with it is extraordinary small. It's all supply and demand.
There are people you've never heard of earning six or seven figures a year from music for ads.
And so on.
The catch is these people are very, very good at what they do. They're not bedroom wannabes.
As for pop - that has always had a complex relationship with management and funding. Everyone assumes you join a band and get famous. But many bands/artists were treated more like investment vehicles or startups, with record companies and sometimes private individuals providing seed funding for careers.
It's a much riskier career than software, where you can be pretty mediocre and make a good living.
But impossible and nonexistent are both spectacularly wrong and absolutely detached from how the industry works.