Personality traits that are not advantageous in some way are unlikely to be maintained over many generations of evolution.

Personality traits that are universally advantageous would not be discernible as traits, because they would become universal to everyone.

Therefore, all personality traits must also be disadvantageous in some way.

So-called "dark trait" behaviors obviously confer advantages at least in the short term. In the long run, we're all dead, but early success compounds, like interest.

Some of the luckiest psychopaths will end up at the very top, while some of the unluckiest will end up six feet under.

This is difficult to accurately capture in statistics, but the expected gain from "dark triad" traits across the whole population is probably zero.