my own experience with DOs, and the healthcare system in general, comes from a congenital myopathy that causes both chronic and acute problems intermittently. For me, treating symptoms IS preventive care.
What I've found is that our system is more than willing to create new professional certifications to handle primary care. As a result, I have experienced nurse practitioners, physicians assistants, and DOs. I am sorry to say the lack of medical training in the first two groups is noticeable, and they are defensive when you question their judgment. Furthermore, they are trained to not order tests or write a prescription for financial reasons, not medical reasons.
DOs, by contrast, have the medical training that truly is necessary for competent primary care while also having the wholistic training that enables them to explain your chronic condition to you without having to rely on tests unless there are real signs of acute problems.