IOWs, according to your statements, recorded rates of schizophrenia have changed because the diagnostic criterion has changed over time. Which makes the author’s statement a matter of differing means of analysis of the history of its diagnostics not an opinion. It also means that recorded rates are unreliable for making any comparisons over time, pro or con.
Your evaluation of my statement is correct.
An acquaintance of mine and friend of my wife was the chair of the committee that formulated the DSM or Diagnostic and Statistical Manual of Mental Disorders. He got the royalties on the book sales.
I’ve heard him lecture many times at Hospital Psychiatry Grand Rounds on the changes in diagnosis over the years. It is always shifting by being combined and some diagnoses being eliminated due to current political trends.