I think what you describe is really overblown - i know many computer illiterate people and 99% of the issues they have with their PCs is about what will happen if they Like something on Facebook or Microsoft forcing some update that takes ages to finish in their $250 laptop. The same people also run Android (which allows 3rd party installations) and they never had any issues with malware - largely because they never install anything outside the Play Store (something that explicitly requires turning on an option in settings that they have no idea about anyway). That would work with iOS perfectly fine.
As for the PC, i think what Apple was doing with macOS until recently (allowing you to run unsigned software you downloaded from the Internet by doing the "right click dance") was a perfectly fine compromise between security for computer illiterate people and still being in control for people who know what they are doing.
Nothing about Apple's model requires Apple to be the only one who can say what you can do with your own device - you can still have Apple be in control by default but also provide a way to take control yourself if you know what you are doing.
As for the PC, i think what Apple was doing with macOS until recently (allowing you to run unsigned software you downloaded from the Internet by doing the "right click dance") was a perfectly fine compromise between security for computer illiterate people and still being in control for people who know what they are doing.
Nothing about Apple's model requires Apple to be the only one who can say what you can do with your own device - you can still have Apple be in control by default but also provide a way to take control yourself if you know what you are doing.