This excludes Debian where the package manager is too complex and packages deviate from upstream too much
This isn’t even remotely true.
Also going with Debian + GNOME Software + Flatpak isn’t a bad ideia at all. Unlike Snaps, Flatpaks are fast you won’t notice delays and waste 10GB of RAM for each application you want to use. And at the end of the day you get rock solid Debian + the latest and greatest software as Flatpaks without “deviation from upstream” and you also keep a clean system.