What a grade in a HS course demonstrates varies from HS to HS (and even from teacher to teacher for the same class at the same school). Depending on the amount of grade inflation, the level of diligence required for a given grade can be wildly different. Some schools allow kids to retake exams and resubmit papers/projects. Offer generous “extra credit.” All serve to bump up grades. So how do you compare a 3.5 from a high inflation school to a 3.5 from a true grade school when you don’t know which one is which?
Retaking the same test or resubmitting a paper/project is somehow better than knowledge of a particular historic subject that was covered on that year’s AP exam or a rhetorical trick (whether right or not)?
AP tests at least provide a basis for comparing kids from different schools. Its true that different kids have different opportunities to take AP classes/exams. But that is true of many other aspects of college applications. Its something of an apples to oranges comparison (or at least a jonathan versus honey crisp comparison) for all of those reasons. And yes AP exams are taken on one date but so too are ACT/SAT/SAT2 tests. Different kids have different opportunities in terms of prep for those too.
I don’t think its a coincidence that the “AP’s are not good enough for X college” approach serves to preserve revenue.