alt Hacker NewsNix comes in because im tired of dealing with procedural solutions to things that should be solved declaratively. I run NixOS everywhere I can because I can actually reason about what is installed on the system. "Package management" like apt and pacman and even app stores has never done it for me.
As to your other userspace concerns... these are all solveable. Perhaps with some elbow grease, but devices like the Steam Deck prove that mobile linux isnt as much of a problem re: userspace as you claim.
Ed.: I'd also like to add that the fuss around security is _mostly_ Google propaganda. Android is not meaningfully more secure, _without application level changes_ than Linux.
SteamOS, very similarly to Android, entirely depends on a corporate benefactor leveraging a parallel user space that happily bypasses the "normal" community-supported parts of a typical Linux desktop distro wherever they present an obstacle. It proves that a company with deep pockets could indeed create a new mobile Linux distro (by writing lots of checks and cutting out large chunks of desktop Linux in favor of custom implementations entirely under their control).