Maybe you're right in some fundamental way, but as an example iOS, macOS, Android or Windows are all considered stable and efficient, secure and highly performa

Maybe you're right in some fundamental way, but as an example iOS, macOS, Android or Windows are all considered stable and efficient, secure and highly performant by most end-users. As a specialist one can quibble and point to counter-examples, but all of these are fine choices. The only big differences are in privacy and level of control offered. It's more likely that by the time Rust makes an impact in Linux stability and performance - because you're using an OS, not just desktop environment - nobody will even remember what System76 was.