The Satipatthana Sutta explains all four foundations of mindfulness, the breath (not anapansati specifically) is only mentioned in connection with mindfulness of the body. Of course it’s an important gateway sure, a good friend along the way no doubt. Sure it’s not uncommon for people to not appreciate the progression laid out in the anapanasati sutta but that doesn’t warrant equating it with the purpose and foundational teaching of the Buddhadamma.