I fell for the lie of flatpak not being bloated, I just nuked flatpak from my PC since I just run arch anyways. Im not sure if repo is safe to remove. You might be able to run rmlint -g and see how much data can be deduplicated on an FS level, I never checked myself since I run f2fs, but if you run an FS with dedupe capabilities it may work for you.
It's not as dramatic for me but it's still bad. I myself freed at least 20 Gb from my computer when I remove flat pack and all of its crap. and migrated my apps to aur myself.
Firejail has some major vulnerabilities if you want to be secure. Bubblejail would be preferred but it has even less documentation not to mention presets like with Flatpak. So you need to sandbox every app yourself afaik