The heart of the matter is not control of the device, it's about the Apple tax, and how it makes no sense in particular scenarios, such as subscriptions.
Sure enough, the app store services are worth something. Real labor, infra and costs go into it. Although Apple could very well subsidize it, it's not 100% unfair to ask for some kind of fee, such as the fee to set up a developer account.
This fairness argument goes completely out the window in the case of Spotify or Twitter subscriptions, it no longer is related to any real costs made. When you pay 10$ to stream from Spotify, it's absurd to have to pay $3 to Apple for this "privilege". Nothing about the streaming or value delivered is in any way related to the App store. They leech enormous sums of money from creators, companies and consumers.
The argument that they're a private company that can do whatever they want is moot. They're an unavoidable ecosystem middleman that affects the entire digital industry. It is insanely hostile to every player except Apple.
The fact that you can't even MENTION an alternative payment in your app should tell you how draconian and power hungry Apple is. You shouldn't cloud your judgement by liking Apple in general or disliking Spotify.