It is not subjective. Its not any AUR user, there are big streams tested especially for that certain system by trusted people before releasing.

And for the record, your sandboxed apps are also binaries and to set it straight, flatpak is mostly not really virtualizing your app. It's complete garbage, have a look at how flatpak achieves this "virtualization" and how it's implemented in 9 out of 10 flatpaks.