Question: Evaluation using tests with high pass rates

I am a physician assistant and I write about the profession. Recently a colleague noted correctly that the way physician assistant schools are ranked is very arbitrary (they survey PA program directors and faculty only). He proposed evaluating programs according to a school's 5-year PANCE exam pass rate. The PANCE is the Physician Assistant National Certifying Exam. It is taken by all PA school grads and they must pass it before they can practice. It is scored either pass or fail. The only problem is, most school pass rates are in the high 90's -- even averaged over 5 years. Basically, the vast majority of PA students pass the PANCE exam their first try without difficulty.

My question for you is: is this a good measure statistically speaking? It seems a more statistically valid method than the survey method (but I'm not asking that). It doesn't seem so valid in a larger sense. In tests that have a fairly high pass rate, is there enough variability to draw decent conclusions about questions like this (the question being how to rank different schools)? What variables factor in your determination? I'm a lay person when it comes to stats, so please factor that into your answer.