Apple provided the hardware, the operating system, the SDK, and most importantly millions of users. A 30% cut seems fair considering the developers don't have to worry about these incredibly major concerns. If it wasn't fair then people wouldn't be developing apps for the platform.

The part that apple needs to liberalize is their policy against sideloading and 3rd party app stores. As soon as the rest of the world catches up to the DMA and side loading is just a reality on iOS all these problems with alternate pricing models can sort themselves out.

You'll find the majority of people side loading apps are those who want to use FOSS only such as fdroid users, those who want to download apps against Apple's current App Store policies, such as people who want cloud gaming clients and emulators, and software pirates. You'll find that it is still more profitable to publish to the AppStore