I first learned about D-K syndrome on Medium a few months back. My life is full of these people AND I was one of them from about 15 to 30 years of age. I think going into business for myself and realizing that I just couldn't wave a magic wand like I thought my former managers could do but were too stupid to do so cured me of D-K. In other words, I got humbled. But I have to be careful as I may still have remnants of K-D in me.
Upon reading this article, it seems there is a grey line between D-K and narcissism. D-K people can be still quite funcitional in many ways and can be managed. Narcissists, well nobody really likes them, and are unmanageable. It would be interesting to see how the psychologists separate these two traits.