Back in the day Ubuntu was sufficiently different from Debian due to Unity. You couldn't get unity any other way, and unity was one of the better DEs. These days, since everyone defaults to Gnome, there isn't a ton of difference between Debian and its derivates, and even Debian and Fedora derivatives. They are all about the same. The only different ones are the ones that are remarkably different, like NixOS or Fedora Silverblue.