The issue you raise about this big pool method is certainly true. I miss however a very important aspect in your whole post: what with record labels? It’s easy to say artists don’t earn enough, but where lies the true problem? This could be in multiple places, and the big pool method isn’t the correct way to pay artists. But I’d actually like to see some concrete numbers of what Spotify pays record labels, and what these record labels pay the artists.
There might be still small indie artists who get payed directly, so my point isn’t true in all cases. But it raises the question if there’s more than meets the eye than the issue you describe.