AP courses may be considered college level but that is only for average schools. The better schools cover more material and skills in courses. UW (Madison) often recommends students who took AP calculus (and “passed” the exam) start with first semester calculus because they won’t be sufficiently prepared for the second semester course. Honors calculus is an entirely different course- son got a 5 in his HS AP calc and the max college AP credits but did the honors math sequence (4 math semesters in 3, theory instead of problem based et al).
You take AP courses because they offer more than other available HS options. Getting college credits frees up your schedule for other classes sometimes. If no credit is given you still have better prepared yourself for your college classes. Your HS AP class taught you something. Never useless to know more even if you take a college version later. Remember- engineers, like everyone else, are so much more than their major.