Whether royalties are calculated per-play-per-user or per-play-per-all-users, I don't see any evidence there's any meaningful difference at all.
Most people who subscribe to Spotify listen to lots of different stuff -- that's the entire point of streaming. Virtually nobody is listening to one song a month, or 2 albums per month. They listen to playlists and radio and their 8,000 liked songs on shuffle. None of the examples you give are very realistic. (Somebody who only listens to one album is just going to buy the album, not subscribe to Spotify.)
In the end, the two models are going to average out to essentially the same.
If you don't think they do, that means you think there's some correlation between the amount of music listened to per month, and whether a person's tastes skew more mainstream or niche. Can you show that's the case, and in which direction? Because that's entirely non-obvious.
(And commercial settings like stores are a drop in the bucket of Spotify subscriptions, they just don't matter. Big places like grocery stores and department stores and fast food don't use Spotify, and coffee shops or clothing boutiques are just as likely to be playing niche stuff.)