The old Internet Explorer full of toolbars, and a notification area with an endless amount of background services, kind of proves the point that the general public are children unable to make decisions for themselves.
As long as the dialog for unlocking your phone would clearly state the risks and what it does, unlike those toolbars upon installation, I think it would totally be OK.
Imagine if you couldnt install Linux on any PC because Dell didnt give you the keys to prevent you from hurting yourself. Or Apple didnt allow sudo in macOS. Seems kinda absurd right? Yet this is the standard for phones.
Also Id like to point out that Android allows installation of external APKs (after activating) and it didnt lead to a super increase in malware, as user still prefer the Play Store, and APK are usually left for the more technically inclined user for niche purposes or often times Region lock circumventing.
Are you sure about that? I pulled an old, cheap Android phone out of storage box to do some debugging. I needed a quick file manager app, installed one of the top results on Google Play that was baked with some malware that may have bricked the device (didn't bother to try to fix it, it's in the bootloader). Granted this was an old version of Android, but that's still a bit egregious. I can't recall anything like that happening on iOS.
https://blog.zimperium.com/new-advanced-android-malware-posi...
-> "Upon installation (from a third party store, not Google Play Store), the device gets registered with the Firebase Command and Control (C&C) with details such as the presence or absence of WhatsApp, battery percentage, storage stats, the token received from the Firebase messaging service, and the type of internet connection. "
It isn't hard to find similar reports, there are enough of them.