I think there are two things going on here....one what we call schizophrenia isn't any one thing just like the common cold is not caused by a single virus but it's effectively treated the same way regardless of which of over 200 viruses caused it. So there is heterogeneity but also commonality...same with sz

The second thing is that to have the dsm definition of schizophrenia you must have social and occupational impairment...if you are holding down a good job and have lots of friends and a mate then any diagnosis of sz would actually be a mis-diagnosis because sz implies social disfunction whereas other psychotic conditions do not. However I'm not sure that this type of impairment is required in the ICD-10 which is often used outside the US so even in this regard schizophrenia is heterogenous...