There's something important the article seems to be getting wrong: psychosis is a symptom, not a disease.
There are such things as psychotic depression and post-partum depression; psychosis is a symptom of severe bipolar mania, etc.
By the way, the concept of schizophrenia first comes up in Emil Kraepelin's realization that bipolar disorder (manic-depression) and schizophrenia ("precocious dementia") are distinct pathologies -- even though they may have similar presentations at times. With this, Kraepelin also inaugurates the idea of differential diagnosis.
Similar in spirit (but less compatible with our contemporary understanding) is Freud's distinction between neurosis and "psychosis", the former being amenable to analysis. I.e. schizophrenia has always been a diagnosis of exclusion.
If people are actually being able to open up schizophrenia into further detail -- well, that's good. But there will always be a diagnosis of exclusion, we'll just euphemize it as "psychotic disorder NOS" or some such.