My experience is different ; Somehow I befriended a bunch of professional opera and orchestra singers in my mid 20s. It is now 20 years later and they absolutely all have side gigs.

We need to distinguish "professional opera singer" and "professional orchestra player" vs Pavarotti though :). Just like there are hundreds and thousands of "professional singers" and one Jennifer Lopez (though one could argue she's a perfect example of side gigs:).

My musician friends teach, do social networks, do all kinds of gigs, and are usually "multi barely employed". Not a single one of them, and two are fairly successful, are "full time employed" in the same sense a corporate professional is :-/.

I think it's a lot about which country you live in. I live in Norway, and went to a music oriented high school (I'm not terribly talented myself, but only half the places were set aside for people doing well on audition, the rest of us got in on grades). A good deal of my classmates became professional musicians of various sorts, two got orchestra jobs. But Norway isn't the best country to be a full time classical musician at all - apparently there are far more positions in Russia and Eastern European countries.

As someone who's been close to several opera singers (long story), I would say that the amount of opera singers who don't have side gigs in teaching or otherwise is very, very small.

Yes, if you're one of the few world famous sopranos you don't need to teach, but most singers are not world-famous. I knew one singer who toured internationally, had sung in front of thousands of people, had sung with world famous people, etc. But who lived in shared accomodation and worked several other part-time jobs to make ends meet.