None of the DSM editions had ever been scientific lmao.
“our understanding of the biology of mental disorders has been slow in coming.”
There’s no biology in mental disorders; none of them have objective phenomena and they are arbitrarily given and created.
Neither the diagnoses nor their criteria are arbitrarily created. Researchers look at clinical data and notice that some symptoms of mental illness co-occur at higher rates that cannot be due to random chance, and when they isolate a group of symptoms that co-occur fairly regularly, that becomes the basis for a new diagnosis. It’s far from a perfect system, but it’s the best one we’ve got while the brain remains the mystery it is. And it is scientific, it’s just on the softer side due to a necessary reliance of “soft” data like self-reporting.