If the content car and track is in ACC, that is where I want to drive it, for me, in VR, the total racing experience in ACC is the state of the art. If ACC had the content I have collected in AC, I would always drive ACC.
Of course, it is not the case, so I drive AC more often than ACC. The variety that makes AC the ultimate sand box SIM, where the only limit is truly your imagination, makes AC my main SIM.
Lately a lot of content, particularly tracks are revisited, updated with the latest CSP magic trick, by an ever growing modding/converting community, making AC evergreen and endlessly entertaining.