There are always tradeoffs. I would argue there are advantages for having a trusted party vetting my software repos. It's why I even use Ubuntu because I trust Canonical to make some sane decisions when vetting their repositories.
You give multiple repository support and suddenly users have to one find a way to add another repo, and second there is no way of removing software from those repositories if they do end up malicious.
Which is why I brought up the webupd8 java instance having root access to thousands of machines.
>users can optionally add more repositories if they choose to do so.
Ubuntu is the version of Linux designed to be used by your grandmother. They want to make it as easy as possible for users to install trusted/safe software from both proprietary/free vendors.
It's kind of telling that Mozilla/Microsoft/Spotify/Jetbrains released software as a snap long before it is even possible on flatpak but nevermind that. I don't think you can even get VSCode, Spotify or Intellij on Flatpak.