Good points! Depression is kind of an activity (to depress), and your view of your situation or metacontext matter more than chemical imbalance in the brain. I do believe that many people suffer from low serotonin in the brain due to many aspect of modern lifestyle (addiction, lot of exposure to screen vs natural sunlight). The chemical imbalance theory is also being propagated a lot due to the huge 'drug industry'. Psychedelics showed very promising results in the 70ties, but all research where shutdown after the invention of brain chemical altering drugs such as SSRI. I am a doctor, but I am personally do not consider psychiatry as scientific. At least in Norway the psychoanalytical tradition is still very strong, whereas talk therapy (is there another world, sounds strange in english) has not ever proven to be efficient. Psychiatry or the medical profession is just grouping people into sick and healthy to justify giving medicine to the sick. As you mention in psychiatry this is just a behavioral symptoms checklist and also pretty subjective. I do not know how we can get rid of the profession of psychiatry how it is today. Maybe the rise in psychiatry is also a sign that something is fundamentally wrong in our society.