I agree. Switching from glibc + coreutils to musl + busybox is much more like "switching operating system" than switching from Linux + systemd + GNOME to HURD +

I agree. Switching from glibc + coreutils to musl + busybox is much more like "switching operating system" than switching from Linux + systemd + GNOME to HURD + SysVInit + KDE. Obviously not. GNU hasn't been "the operating system" in at least several decades.