Perhaps that is the advantage offered by a trait like narcissism.

No, because narcissism does not mean: self-reflection, introspection, consideration for one's own thoughts, pondering ideas, inwardness, etc.

Rather, it would be more like this: I think I'm the greatest. I'm so much smarter than everyone else. Whatever I do will be extraordinary.

Narcissism tends to be empty of substance, because by definition it means an exaggeration.

It doesn't take long to realize that's of no benefit to a process of thinking when it comes to problem solving, invention, or innovation. The more time spent on congratulating yourself on artificially inflated views about your own abilities or accomplishments, the less time spent actually doing. Narcissism is a detriment to achieving great output, to the extent of the narcissism, as it's wholly a waste of thought and time.

I think you just made all that up! Narcissism is orthogonal to achievement, in the sense of having a drive to achieve.