This site has been posted here multiple times in the past. I'd still like to know what the author suggests the alternative should be?

I'm a Qubes OS user, which indeed is a much better solution in terms of security, but it comes with plenty of drawbacks that a lot of users might not be willing to accept. It's also difficult to use for people who are not interested in security.

Right now, there is literally only one project in the Linux community that even tries to address the enormous hole which is Linux security, and that is indeed Flatpak. It's not a perfect solution, and they still have some way to go, but there really is no other way unless you want go to Qubes OS.