Isn't this true of nearly all mental disorders in DSM-5 and ICD-11?

We don't really know what mental disorders are and so we don't have objective diagnostic tests for them. [1]

We just have treatments that sometimes work for some people (and with the replication crisis[2] that sometimes is probably a lower value than expected).

[1] https://pmc.ncbi.nlm.nih.gov/articles/PMC6732705/

[2] https://pmc.ncbi.nlm.nih.gov/articles/PMC5835722/

I concur that many of the diagnostics methods are small sample sized for psychological tests. However I believe we have a lot more neurological evidence for underlying conditions and mechanisms in some. Schizophrenia for example has clear neurological hypothesis relating to agency and we can clearly tell these patients in a standard MRI. The same cannot be said for ADHD or ASD