And the premise of your statement is that only pro musicians deserve to be compensated for their work. That’s a pretty messed up world view.
*not only Spotify
They had plenty of problems from people abusing their system to steal listens from actual artists.
Their system is basically "one big bucket of listens" - if your song gets listens, you get money. So if you pay your sub, and listen to say 5 niche musicians only, it still all goes mostly to the most popular songs.
Now you might already notice the flaw here - if you say, make a bunch of bots that just listen to songs to boost their revenue, not only your sub doesn't pay artists you listen, but also to fraudulent ones.
Then there was problems with using fake collaboration tags, AI music to hijack artist profiles, and few others.
That's basically how radio is accounted for in royalties, as well.
With Spotify knowing exactly who listened to what, it could be more precise (and arguably more susceptible to the fraud), but tbh what they do is standard (compulsory licensing) industry practice.
If either of those was true with spotify, the unfairness would go away.
But when different listeners are paying very different amounts per hour, any correlation between payment amount and preferred content causes problems.
These big platform payouts matter a lot.
When you read artists' blog posts you can see they get peanuts. Not due to Spotify - due to the recording deals.
If you want an exhaustive but eye-opening account of all of the details, I recommend "All you need to know about the music business" by Don Passman.
A quick search suggests a very steep drop off from the top earners.
‘At 100 million streams, artists can earn approximately $300,000-$500,000 in gross royalties. However, the actual amount reaching the artist varies dramatically based on their contracts. Major label artists receive $90,000-$150,000 after the label’s cut, while independent artists could keep $255,000-$425,000 after distributor fees.’ https://rebelmusicz.com/how-much-do-artists-make-on-spotify/