I completely understand the argument here, but the problem is that there is no other option. I think that there is a middle ground here if Apple allowed users or apps (i.e. a secondary app store) to install other apps without going through the Apple app store. If you want to stay in Apples walled-garden you have that choice, otherwise, install your own apps.

There are arguments about how well this works in the Android ecosystem, but I think that simply having the ability to do it, even if inconvenient is a world of difference than being beholden to a single entity. Imagine if Windows only allowed you to install apps from its app store. You could make all the same arguments that it should be able to do this just as you would for the Apple store.