The swith that “disables everything that can be disabled” is the power switch…
Maybe you have your conception of wath you want desable but it’s not universal.
This is not a rational approach, unlike the choice made by Purism. So if you want to be able to control all the devices without imposing your own choices you need more than 3 switches.
An illusion of assurance, not a real assurance, read previous answers.