The hard truth in music (and in many creative industries) is that there's a huge oversupply (many musicians are willing to make music for free or very cheap) and demand has a low willingness to pay. The result is that there isn't much money to be made for musicians. In my mind, there's really no way around this fact. You can argue (as these folks are) that Spotify could take a smaller cut and give more to musicians. While this is technically true, Spotify is never going to do this. It's a strictly distributive transaction: musicians make more money, Spotify makes less.

Their other options are not so good either. Musicians can build a Spotify clone that's more favorable to artists. Nominally, this sounds like Tidal. The problem with Tidal is that nobody wants to spend that much money on a subscription. Even with the high profile artist exclusives it has less than 5% market share. Beyond the business model, building a Spotify clone is difficult to execute, especially for musicians and not software folks.

You can somehow lobby to outlaw streaming and go back to selling songs and albums individually. This would definitely hurt Spotify but probably doesn't help musicians too much. Potentially the top 1% of musicians are better off as they're able to capture more value but the long tail is way worse as nobody discovers their music anymore.

An interesting solution might be collective action. If enough musicians banded together and pulled their catalogs from Spotify, I could see that having a big negative impact on Spotify's revenue. There are a few bands that if their catalogs were off Spotify, I'd probably cancel. This would be effective but is probably too difficult to coordinate.

Overall, the problem for musicians is one of economics. Too many people willing to make music, not enough willing to pay. In other words, you can't push a rope. If you are a musician, my strong advice to you is to get comfortable with doing it for a reason other than money. Otherwise, you're in for inevitable disappointment.