I've seen a lot of therapists badly misdiagnose what are complex psychiatric illnesses. My current therapist ALWAYS defers to a psychiatrist when diagnosing psychotic disorders. Psychosis is complex and therapists don't have the medical training or experience to diagnose correctly.

I was diagnosed my a PhD psychologist as having schizophrenia. The diagnosis got in my electronic medical file and wreaked havoc in my life. My psychiatrist and I had to clean it up. What I have is Bipolar 1 disorder with psychosis, DID with a psychotic part, and PTSD with psychosis. My PhD psychologist was incompetent to diagnose psychosis that complex.

The lesson I learned, let the MD do the complex diagnosing.