At UGA we teach calculus to freshmen in classes of 35 or less. I have 16 survivors right now after after 18 AP students droped out, of the non honors class. So thigns are different everywhere, but I obviously have more experience after 40 years of teaching at the college level than many people.
I agree with you that the appropriate course for a good AP student (surely you realize that most AP students did not elarn anything, and provide the bulk of the college AP enrollment), is to retake the calculus at an honors level.
Nonetheless many of us from the 1960's entered college with no caclulus and took rigorous real analysis level calculus courses, such as Spivaks book was written for, and Apostol. These books ere written in the 60' for beginning calc courses for students with no calc background.
My first freshman homework set asked me to prove e is irrational using the taylor series, and to calculate it by hand out to 9 or more decimal places, i.e. featured both high level theory and detailed calculation. By the second semester we were doing abstract vector algebra and several variable calc and differential equations, including hilbert spaces. The sophomore course was on manifolds (Loomis - Sternberg), much higher level than the berkeley book I taught out of to hs students.
I will not evaluate my own hs teaching, and some parents of unsuccessful students called it "simply bad teaching", but some of the students were certainly excellent. Of the 6, one of them is now a well known full profesor of math at an ivy league school, and another was phi beta kappa at harvard and took a phd in physics before changing fields. he said my course was essential to his survival in harvards sophomore math course from raoul bott, and he did not take the loomis sternberg version.
all that is necesary for students to learn advanced material is to want to, and for the teacher himself to understand te stuff. this is what is missing formhigh school AP courses usually. Having someone teach AP who took calc in college is very diferent from having an international level researcher teach it. I have also taught eulers characteristic for polygons to third graders, using models, and one of those students, became an astrophysics major and aeronautical engineer.
It is not harmful but good for young students to be taught something deep, if it is fun and intellectually stimulating. Other hs students i have taught did projects in galois theory before going to such schools as mit.
as a teacher i had some serious failings, which i mention for your use as a teacher yourself. I did not praise my students enough, and I did too much explaining, instead of letting them do more for themselves. Those failings are still visible here. But my enthusiasm went a long way, and the beauty of the higher level material had its own fascination for them.