(sorry for my english) As a psychologist I love your post. The first paragraph it's so relevant to understand, when we are discussing "disorders" and not a disease. Epistemology often view as purely theoretical, it's essential for this kind of discussion.

For anyone interested in this topics, the essay in the Stanford encyclopedia of philosophy is pretty good. https://plato.stanford.edu/entries/mental-disorder/

A less technical discussion https://www.npr.org/2010/12/29/132407384/whats-a-mental-diso...