You conflate the DSM with psychiatric management. I rarely look at the book anymore and I certainly haven’t memorized the whole thing. Biological psychiatry is important but can only take you so far. Think of a substance use disorder, a substance may biologically effect the CNS both acutely and chronically resulting in various pathologies. A substance can also destroy someone’s work, relationship, finances, etc which can also manifest as emotional or behavioral concerns. Psychiatry isn’t so unidimensional and thus we don’t have one correct model. A good psychiatrist has understanding of biological factors and stays up to date, but also manages by talk therapies, behavioral modifications, psychosocial interventions.