Atomic desktops enforce immutability, the core system is literally a ROM almost like stock Android. It's not always bad, I can easily imagine cases when it is perfect, but it's not what I'm currently seeking from Linux. As far as I could figure out, secureblue imposes slightly less restrictions.
Yeah well I knew about Arch circlejerk, but these KDE guys are something. I would probably get same reaction asking an Arch community about how to purge pacman.
NixOS is worth testing indeed. However, AFAIK it is not lightweight enough for my setup. Pretty same as Gentoo, I guess. It is kind of ironical that the most controllable and efficiency-oriented distros aren't actually good for mediocre setups (but well, I believe nothing stops from building a system on Gentoo with a powerful setup but with flags targeting a low-end device and then flashing the result to the latter). Unfortunately I have no experience with programming, so my learning curve will be fairly steep. But one day I'll just have the required skill level even for managing NixOS. And probably I will even learn programming, who knows.