So, now you claim that the advantage of “APA” definition is that it is “standardized”? That’s it?
I’m afraid that’s not worth much.
Certainly not enough to outweigh the impossibility of “mild form” - the disadvantage you ignored.
Oh, really? Why?
Take up the Catechism and find what kind of sin is supposed to be that. After all, it is “standardized”, and used by “spiritual health professionals”.
Oh, and, naturally, I assume that we are not dealing with using something else while claiming to be using standards of APA. That, of course, would be lying.
Are you sure he has to determine what is true and what is false? It is sufficient to take a realistic (humble) view of his own profession. He is not really much of a “mental health professional”, he is mostly just a man who is willing to be paid for listening to other men. That is already a useful role: sometimes that really helps, and not everyone is willing to listen to insane people, even for money.
But those “mental health professionals” must not think that they actually know much about “mental illness” or “human psychology”. No, they generally know as much about all that, as anyone else. When they think otherwise, most of the things they “know” are false (see that article about psychological research), and, therefore, in those cases opinions of “mental health professionals” on “mental health” rank less than those of random strangers.
Perhaps Chesterton’s “Eugenics and Other Evils” (http://www.gkc.org.uk/gkc/books/Eugenics.html) would be somewhat relevant: “The second thing to be noted is this: that it is only by the unanimity of sane men that we can condemn this man as utterly separate.”, “That which can condemn the abnormally foolish is the normally foolish. It is when he begins to say and do things that even stupid people do not say or do, that we have a right to treat him as the exception and not the rule.”.