This is not my opinion, but critiques against AP classes point to the correlation between the resources a high school has and the amount of AP classes and resultant tests available. More focus on AP classes would likely exacerbate economic inequality in admissions (so the [not my] argument says).
AP classes aren't an inherent problem if they're providing longer duration intensive study for more advanced students. There is, however, no reason for an external testing industry to validate a student's knowledge in fine grained subject areas. I went through high school before private testing had metasticized into its current form. AP classes had the benefit of a +1 bump in GPA. Nobody was left standing at the gate because of lack of resources.