There’s no right answer, it comes down to the individual and what they think it’s worth. If you’re not getting enough from spotify(no surprise), than you can move your music to Apple, who tends to pay artists a bit more. If you still don’t think you’re making enough, look into one of the many independent platforms and see if you can make what you feel you deserve, like Tidal.

It should also be noted that you can’t use any past numbers as a metric, since technology has vastly changed how we can connect to the artists we enjoy. In other words, there is no physical product to account for so you can’t use numbers from sold CD’s, tapes or records as a metric.