If Flatpak security is this much of a joke, why do people go through the trouble of using it? Flatpaks are outright cumbersome, and bar-none my least favorite way to install anything. Have a local GTK/Qt theme/colorscheme? Gotta manually patch it in. Have a small main drive? You can store maybe three or four Flatpak'd apps. Slow internet connection? Good luck, you'll be here a while. All of it boils down into the outright worst way to distribute software on Linux. I'd rather use Snaps, which should be taken as a violent insult to anyone who's familiar with the medium. Nowadays, if I see that an app is exclusively distributed through Flatpak, I'll compile it from source or find an alternative.
The future of software cannot be containerizing anything dangerous or complicated. All it does is add an extra layer of abstraction that makes it harder for the end-user to use your software. All of this seems especially redundant on Linux, where we could take any number of extreme measures to sandbox software. Why did we choose the path of most resistance for the user?