You are mistaken. I am still in the media industry. I have direct access to data and have close friends who manage artists and labels.
The reason why small artists earn proportionally less is because of (or lack of) concert tickets and merchandising. Those are
up to 70% of a signed artist's income. Small time artists does not have that income.
However, this is changing with TikTok. Now anyone can earn big bucks if they have a big follower there. This is very new, a couple of years old if that.
There is no major artist that have a meaningful percentage of their income from disk sales -- full-stop. Times have changed. Even Adele has to go on tour as her streaming numbers are less than a third of what was.
If you want to know what is the state of the music industry read
what my friend says and/or subscribe to his newsletter.