Labeling 1/3 of everyone narcissists isn't helpful either. Every human has a balance of narcissism and self-loathing in them, and you can find narcissistic traits in nearly everyone if you look hard enough (ask leading questions in a survey). NPD is important bc it indicates harm.
1 in 6 people isn't a third of anything. Your math isn't mathing. And I'm quoting experts in the field, I'm not making anything up. And my degrees are in psychology. NPD is harmful but also rare. The vast majority of narcissists are not malignant narcissists. The diagnosis is misleading.
And NPD is rarely diagnosed formally because narcissists don't seek treatment. They think everyone else is the problem, not themselves. Narcissism is a maladaptive coping mechanism rooted in deep-seated insecurities. Left unchecked it becomes a serious personality disorder. And it has many forms.