Here's the combined score distribution data for all the Advanced Placement examinations.

There's a countervailing consideration: a low cutoff for a 5 means that one could in principle achieve that cutoff by understanding some subtopics of the syllabus very well and ignoring others entirely (for instance, many AP BC 5 students may be very thorough with derivatives and integrals and have marginal knowledge of series). This is most so if the test question are individually hard and the students know in advance what fraction of the test covers what topic(s). To the extent this is true, it points in the opposite direction to your concern once we consider specialization within subjects.