FYI, flatseal is in the arch extra repos, so it could be one less flatpak you use 
Back in my Linux Mint days, Flatpak was my go-to for replacing old Ubuntu-based software. After getting tired of sandboxed permission issues, crappy theming, and Ubuntu in general, Iām on Arch for good. I did run a few KDE-based Flatpaks (okular was the main one) when I was still on EOS Xfce.
Not using flatpak for anything currently but have used it in the past, most recently probably when I was using Bottles for Fallout and managing its mods.