Here the "broad conclusion drawn" is that depressed people see the world more realistically -- which if true could have sweeping implications in many areas of life (e.g. they would make better stock pickers, they should be put in command of armies).
The single specific experiment is a 1979 study on correlation between a light bulb and a button. Has this study been replicated? Is the result robust to trivial variations, like predicting a biased random walk, or a continuous correlation (like how hard someone hits a pad versus how many lights light up)? Where's the literature review article for the broad conclusion? (Oh right, this is Vice!)
Now that the nitpick is out of the way, suppose the conclusion is true. A thought experiment would be would a person who estimates light-button correlation accurately be the best at a particular job?
If you wanted to get the best statistical estimate of a correlation, then the more realistic estimator is best for the job. But imagine a situation where you press a button and a green light would light up 10% more often if you press the button versus not. If your goal instead is to get the maximum amount of green light, you'd actually want the person to be pressing the button as often as possible. You'd actually want the person who overestimates his own effectiveness because he'll put in more effort and yield better results!
Generally speaking, it's possible that someone who moderately overestimates her own effectiveness in the world will be better at getting things done in the world, versus the realistic estimate.
Partially related, but I'm reminded of Elon's quote: > I’d Rather Be Optimistic and Wrong Than Pessimistic and Right