What’s supposed to happen, if you click on the small box tagged “primary” in the window, where you add aliases? I tried. Nothing visible happened to the order of the aliases.
I just tested it and you are right and it doesn’t work. Looks pretty though!
That is a mystery to me too.
I wasn’t part of the project when the schema was designed, and I’ve wondered what the potential uses for it would be.
Theoretically, it allows you to define what is the canonical name (and script) in each language. That being said, it isn’t currently used for anything, as you’ve found out.
It will eventually be used to sort aliases.
I would have thought the primary is the original language title of the Work. I can’t see the point in sorting the order of the aliases. Maybe someone can suggest other uses for this function.