Fair enough. Although experience shows that some packages with assigned copyright are barely maintained (even in Emacs's core), so obviously that's no silver bullet.
My perspective is simple - don't mess with something that's working well. (e.g. you're getting many occasional contributors on GitHub and you want to keep it simple for them)
> I have to say I'm a bit frustrated that every time someone wants to submit something to NonGNU ELPA there's some push to either submit to GNU ELPA or core instead.
Some of us believe that assigned packages are often better for the
overall health of the project, so we continue to argue for it. It
would be irresponsible not to.