Musicians were definitely dependent on the upper class. Some were wealthy, some were not. Just as today music served the role of entertainment, although public concerts were a very new thing. They appeared only at the end of eighteenth century. In short, music (at least music of the famous composers) was largely reserved for the privileged.

Composers often worked for royalty, as Mozart did, and were quite rich and high in society as a result.

the music was the role of Mozart's time