In my high school in the 1970s, if you wanted any serious instruction, AP courses were your only option. Nevertheless, I never sat for any AP tests; my university had no required freshman courses to place out of, and I never sensed that any prerequisite courses were likely to waste my time. It was all I could do to keep up with a full course load at the suddenly much more challenging level that awaited me after I left public high school. The AP high school courses nevertheless were quite good, an adequate preparation for a rigorous university, if not necessarily a substitute for freshman year. If I had chosen to attend a state school, I might well have placed out of many freshman courses, since many of them amounted to remedial high school instruction.
This AEI article claims that AP has succeeded notably in expanding its market reach during the last decade or two, without sacrificing its quality control. There have been reports of PC nonsense influencing the exams, but the overall rigor remains high.