Also if we use atomic distros with flatpaks and whatnot that mimic Android security the end user basically ends up having to essentially use Termux (but busybox or something similar) on their Linux phone as well
GrapheneOS makes our own major improvements to the permission model, but we cannot enforce apps adopting it and need to design it all to be backwards compatible. We do that for Contact Scopes, Storage Scopes, our Sensors toggle and other features but not everything can be done that way. For our exploit protections, we have toggles to work around apps with memory corruption bugs or bad practices such as dynamic code loading. Android can enforce apps improving in a way we can't do. We're starting from a platform with a mandatory app sandbox and relatively modern exploit protections though. Android also does support using hardware memory tagging or HWASan to test apps even though many developers aren't using those to clean up their memory corruption bugs.