Nonsense!
I've been severely depressed, and I didn't think as rationally as I normally do, although for me it was reason that eventually gave me the grip I needed to climb out of that pit.
Others have talked about their severe depression, and how it changed their thought processes for the worse.
You sound like alot of people I know. You read this or that article, maybe a case study, whatever. And you are painting with a broad brush, but the thing you are trying to paint has lots of tiny detail. *SLOP* there's your version of reality.
I can imagine some circumstances where the beginnings of depression or it's aftermath might be associated with some enhanced insight as a side effect of a sense of detachment or something, but the general case is quite the opposite.
In fact, the term "depressed" originates as a term describing the nervous activity of the patient! Their nervous system was deemed to be functioning at a diminished capacity. Google the symptoms of depression -- darn near a complete list of brain-center by brain-center functionality, all under-operating.