iPhone users (like myself) need to look no further than the Mac to see what a better alternative might be. The Mac only allows App Store or signed apps to be installed by default. However this setting can be toggled to allow any apps for those who need that. You can also toggle it to allow only vetted App Store apps if that’s what you prefer.

Apple could keep the default to what it is on the iPhone right now, but should at least allow signed apps from other stores as a non-default option, even if they don’t allow unsigned apps at all.