monolithic monopolies
Artists are angry at streaming services for turning into monopolies, but what they are really angry at are their decreasing profit margins. Streaming services like Spotify are not monopolies. They are utility apps that are finding it increasingly harder to distinguish themselves. There is an intense competition and that is precisely why they (and in turn the artists) have low profit margins.
The real monopoly is Apple who owns the platform which hosts all the music platforms which in turn host all the artists. Two years ago Apple launched its own streaming service, severely undercutting the incumbents' prices. It could afford to do so because any move increasing their hardware sales justifies itself due to the fat profit margins there.
Nested market structures do not lead to polylithic monopolies, they lead to monolithic monopolies where each level is dominated by the same entity which dominates the lowest level.