I really like flatpaks to install desktop applications, as mentioned in some other comments the sandbox is sometimes poked full of holes because some applications don't use XDG desktop protals and need full filesystem access. If you are really concerened about this, you can use flatseal to limit the access that the application has.

If you prefer other ways of installing your software, that fine. But I really hope flatpaks continue improving and become the de facto way of installing desktop applications across all Linux distributions. For a normal, non-technical user installing and updating software should be easy, and I believe that flatpak provides this.