I have a similar 5.7" 32 GB eMMC device that runs a debian-ish distro with Phosh GUI, where I have been installing flatpaks left and right (without caring which runtimes they use) for a reason ([0]) since early 2022.
I am now at 107 total flatpaks, 18 of which are platform packages (= 89 apps+locales). If I were to remove five outdated apps, that are archived or inactive upstream, I would be able to get rid of four platform packages (I really should, but I don't want to for sentimental reasons).
I have found things to scale similarily across devices: The more flatpak apps you use, the better the ratio gets.
If you just use one app, you may end up with 3 Platform packages for it if you are unlucky, making that one app an incredible disk space eating monster. When you have 50 flatpak apps, things will look way better.
Now, would I like to have all these as native deb, rpm, tar.xz (arch), apk? Yes.
But I would also like to use the latest version, making that pretty much a pipedream - and in some cases the distro packages (mostly on Alpine and the AUR) aren't always as functional.
I am really glad flatpak and flathub are a thing.
OT, regarding alternatives discussed in other threads:
AppImages aren't really a thing on aarch64 (also, I use Wayland, which probonopd does not seem to be a fan of [1]).
Snaps: I had 'wrong arch' failures when attempting to run what was promoted as arm64 on Snapcraft.
[0]: https://linuxphoneapps.org
[1]: https://gist.github.com/probonopd/9feb7c20257af5dd915e3a9f2d...