According to Spotify's data report site[0], there were 17,800 artists grossing over $50k from Spotify (7,800 being between 50k and 100k), out of a denominator of ~8 million, or 200k if you use Spotify's estimate of “professional or professionally aspiring”.

I don't know much at all about the music industry, so I don't really have a conclusion from those data, but that seems low. It also does put a (not insignificant) number on the independents accomplishing what you describe.

0. https://loudandclear.byspotify.com/