I can say with relative certainty that the roots of my depression have nothing to do with chemicals in the brain.

I think the basic confusion comes from the way psych drugs were first developed. For example with the earliest antidepressants it was noted that serotonin processing was impacted. So researchers reasoned that serotonin must be the cause of depression. But further research showed it was not so. The story stuck though, precisely because it made biological psychiatry appear to be a legit form of medicine, and that its new pills were like antibiotics for infectious disease or insulin for diabetes. When people take the drugs, they experience changes and assume the "medication" is "working". But the effect does not prove the theory. It's actually the reverse--the drugs introduce a chemical imbalance.

If it works for someone, that is great, not knocking it. My own experiences with SSRIs (admittedly brief) were not positive.