alt Hacker News> dislike flatpaks and favor a low-level, bare-metal approach
Flatpaks are sandboxed with bubblewrap[1]. I would still call that bare-metal. And flatpaks aren't particularly bloated either, there's no need for a flatpak to be any bigger than a regular binary if it only depends on the kde/gnome/freedesktop runtime.
I used to prefer installing apps via my distro directly, but I now prefer using flatpaks because of the way it sandboxes the applications. When I delete a flatpak I know for sure any configuration or cache files for that app are also gone (unless you opt to keep them).
If you want to play with atomic distro's, there's a bunch of different approaches out there. For instance GnomeOS is not package based at all. OpenSUSE works via btrfs snapshots, Fedora Atomic uses rpm-ostree currently.