Well how do you define how much control is enough? You can still download Fortnite and put it on your device, just through the app store.

If every Tom, Dick and Harry could setup an app store for the iPhone, this doesn't necessarily give me more control. It might mean I am then forced to use the Epic platform for all Epic related products. Now how do I know that Epic have appropriately vetted their application? What if they start producing applications for the iPhone which are terrible?

This is a big problem on the Google store whereby plenty of the apps are rubbish.