Recently switched to using Flatpaks instead of random .debs for a number of apps on my system. /var/lib/flatpak takes up 7GiB, which honestly isn't that much (even though it's like quarter of the OS size), given that's the software I use most of the time.
Was skeptical at first about Flatpaks, but SteamOS showed me that is great at just giving OS developers access to a fully populated app store with minimal work.
Honestly, nowadays I'd say "ability to install flatpaks" should be the criteria on which we decide whether an OS is really "linux" or not (that is, SteamOS is, but Android isn't).
Edit: Okay. I said something stupid here, my bad. What I was trying to get at is the distinction between Android, etc. and "Desktop" Linuxes like traditional distros, Chromebooks and the Steam Deck. Even though it technically runs Linux, it's hard to argue that developers for Android are really writing apps that work on "Linux". Wheras if someone releases a Flatpak version of their app because they think the Steam deck is cool, it works on other distros "for free".
Yup, Flatpaks are indeed great. Isolation, modern versions, no weird dependencies.
I have to manage a Debian PC fleet and I am too stupid for Ansible, so they all just got cleaned up extremely, all that bloat gone, apps replaced with flatpaks and now the system has like ⅓ the packages. Automatic updates then, VirtualBox is the only stupid thing with their kmod and all, but Virtmanager is also already on there.
Not all apps can be flatpaks, for example virt-manager, gnome-boxes can but its really restricted then.
But keeping the system slim just makes so much sense, its like removing this distro randomness which I am sure is needed for Linux to get their shit together and stop doing the same work at 10 different places.