It is not a strange premise. It is the security model that for example Android uses. Unix security model is dated, and it is good that steps are taken in this direction.
Are you actually suggesting that most Linux desktop users only use the same 4 programs you do and will never use or install anything else? If that's the case then why bother with a display server or package managers? We can hardcode those 4 programs into the system, have them draw directly to the framebuffer and then we can remove the ability to install any other programs. Sound good to you?
The point is to reduce the attack surface, especially for browsers that run untrusted input. You don't want a local exploit in your browser (that hopefully is also configured not to have access to your entire filesystem) to screenshot other apps and websites.
Maybe you disable all the warnings in IntelliJ too that prompt you to be careful when opening a new Git project from a remote source?
