Read this article to learn how $ payouts per stream are determined: https://www.hypebot.com/hypebot/2022/02/music-streaming-real...
It's all pro-rated. 52% of Apple Music revenues go to labels, by contract; Spotify is around the same. Royalties are just revenues divided by # of streams (simplification).
Spotify's free users give lower royalty rates per stream, and Premium users give higher ones. If Spotify users like rap more than AM users, then rap will have higher rates on Spotify than Apple Music, since a larger proportion of revenue will go to the same amount of rap songs.
If Apple Music is more painful to use than Spotify, or has worse discoverability, then people won't listen to as many songs (or won't leave it on for 8h as background noise) as with Spotify, and royalties will be higher per stream than Spotify. The higher royalties don't make up for the lower # of streams since discoverability benefits small artists.