GPA is about as flawed as alma mater, but I think combined they give a useful signal.
It seems to me you should ask questions you expect the candidate to be able to give good answers for, period.
I've heard that Harvard is similar: the grade distribution at Harvard is roughly 10% As, 80% Bs, and 10% Cs. Getting an A at Harvard implies that you really did a lot of work, but getting a B could imply everything from "You really did a lot of work but just missed the cutoff" to "You learned basically nothing from your undergraduate education."
Or maybe they learned exactly what they needed to do to game the system. Does doing a lot of work correlate to learning more? Seems both sides of the huge distribution got the same perceived outcome, just one did it easier.
It's inflated, but then again, how much Harvard coursework mastery is actually necessary for your job?
Mastery or not, if your score bumped you out of the curve, you were getting a B.
Friends in Ivy League schools would get As or incompletes.