Current wisdom holds there is no schizophrenia rather there are multitudes of schizophrenias. Basically current wisdom holds that in any diagnostic category there are multitudes of illnesses with different etiologies rather than single illnesses
I would argue that all mental illnesses arise due to epigenetic dysregulalions of TET enzymes, JmjC domaining containing proteins and dysregulation of acetyl-coenzyme A synthesis which can dysregulate histone acetylation. There is only a single mental illness.. There are many, many expressions of the single mental illness due to epigenetics. Various epigenetic dysregulations channel other epigenetic dysregulations giving rise to distinct illnesses. The same treatment could work for all mental illnesses though only subsets of the treatment could be needed for some illnesses.
This is actually quite a hopeful time in research on mental illness. But any breakthroughs likely will not come from psychiatry but rather arise from basic research which is so often the case. TET enzymes and the gut are huge research interests and those are the two areas that have to be researched for there to be a breakthrough.