But the thing people seem to be missing (and that Spotify is deliberately obscuring) is that Spotify doesn’t offer IAP subscriptions on iOS, instead they’re already doing what Netflix is doing. Basically, they want to advertise subscriptions in the app without paying anything to Apple, though I’m not actually convinced that it would lead to the conversion rates Spotify would need to be profitable (Spotify’s problems aren’t connected to Apple, they’re self-inflicted in my opinion, they’ve screwed themselves over with all these purchase bundles, I legitimately wonder what percentage of their customers pay full price for the service).
Exactly.
And they've leading people away from App Store payments since 2015.

Spotify urges iPhone customers to stop paying through Apple’s App Store
The Apple Music rival sends out an anti-iTunes PSA

Spotify is still the largest music streaming service in the world... and that's without having IAP.