Realistically the switch you want exists,
AltStore uses it to put apps on your device that are not from the App Store by utilising a personal signing key that Apple permits you to put 10 apps onto your device and the certificate needs to be refreshed every seven days.
Why it bothers many of us here is that by enabling a third party large scale App Store environment of the likes that Epic is pushing for would start to fragment the apps the same way Epic has fragmented the gaming ecosystem on the desktop. It will lead to situations where companies will make their own App Stores and will put exclusive apps in those App Stores to force people to install them. Many of us don't want to have to deal with having to use the Steam launcher for Steam games, Epic Games' launcher for their exclusive games, EA's launcher because they forced you to buy and launch games through their store, the Adobe updater and all of the crap it loads onto a device and the Microsoft updater that half of the time needs to update itself before it can then update their own apps.
I like that on iOS I don't have to deal with this noise and by forcing Apple to provide an alternative you in fact remove choice from me. If iOS' limited options aren't sufficient for you, there exists a mobile device operating system that provides this capability that is important to you. It is not that you might do something dangerous for your phone but by enabling the functionality you desire, it repeats some of mistakes that other platforms have made.