I'm confused, are you claiming the Epic lawsuit and other controversies are about standalone apps that don't access file services?

The controversy is that Apple wants a 30% cut on services that do have files and infrastructure, and also a piece of subscriber bases that were built outside of the app store.

Apple also demanded companies couldn't have apps if they had subscription systems outside of the app store.

Most people don't have a problem with Apple taking a 30% cut of purchases that they enable, but using their market share to leverage their way into transactions they have nothing to do with has understandably upset a lot of people.