Exactly. It's often useful to have a label to describe a set of symptoms that you see occurring together over and over again, even if they don't always have the same root cause. The problem is when doctors mistake the existence of a label for understanding.

But we don't have that level of knowledge yet when it comes to schizophrenia. The closest I can get to such an absolute is "all schizophrenia cases are similar in that they manifest as sensory inputs uncorrelated to the outside world", but that isn't really a useful classification -- that description is based on symptoms, not on causes.

I think we only have a partial understanding of cancer as well. Uncontrolled cell division is something in between a symptom and a cause.