I wonder if an explicit policy that grades are for internal purposes only would help. That is, grades are useful feedback on how well you're learning, but they aren't comparable between classes and aren't intended to judge or rate students. So the uni would refuse to calculate GPAs or report grades to outside parties.

Maybe they could even give more flexibility on how grades are calculated and reported. Like they could be whatever combination of pass/fail, letters, percents, notes etc that the prof wants, because by policy you're not calculating with them.