It depends on how you define "relaxed", if you mean low CNS arousal as a base state but can easily move into a highly aroused state when needed then maybe.

But if you mean low CNS arousal generally then I completely disagree, someone that pushes to 100% will out compete you if you never breach 50% assuming equal ability. If you and I both have the same capacity for strength but you are an intense person and I am not you will be the stronger one in the short and long term. Same goes for the intelligence question as well.

However modern society short circuits part this general behavior though and all bets are off though I still think it holds true. It is often not the best political or business idea that wins, it is the one someone is willing to push through. Human relationships are similar, an activation energy must be reached in order for mating to happen and someone with a higher intensity is more likely to reach that activation energy more often.