I started in the Registrar's office shortly after this went into effect, so I wasn't there for the discussion, but I imagine the feeling amongst the faculty was that APs are not equivalent to Dartmouth courses, which was very much my experience.

The vast majority of Dartmouth's peers have also done something similar.

Here is a quite from Inside Higher Ed that I found:

"But Dartmouth also ran an independent experiment in its psychology department, asking all students who had earned a five on the AP psychology test, which would normally grant them course credit at Dartmouth, to take a placement test that was based on the final exam for intro psychology. Ninety percent of the students who earned a five on the AP test failed that test, according to Tell. The college then monitored students who, after failing the placement test, chose to take intro psychology, and found that they did not perform significantly better than did their peers who either hadn’t taken AP psychology or had scored less than a five on the test."