[dsego]

> No tests exist which can detect those imbalances.

Yes, but the drugs actually work, which validates the prediction.

> Mental illnesses, in general, don't develop organically from biological defects.

In schizophrenic patients there are clear organic changes in the brain, you can see it on brain scans.

> These things come about because of profoundly dysfunctional psychosocial environments.

Then it would surely be possible to "fix" these issues without pharmacology treatment, which is unmistakably not the case.