Actually having a personality disorder is rare, and very difficult to diagnose. Showing narcissist traits, however, is easier to look for. Not all dubs are narcissists for sure, but the doctrine and way people outside the organization are labeled and judged is to strip away their humanity, so even emotionally healthy dubs see people with a toxic lens that they've adopted.
I agree that not all Dubs are narcissist but the cult attracts those types and cultivates it in them. You are correct I remember the days that I was a dub and I have to say know I am not proud at the way I thought about "worldly" people being less human than the rest of us dubs were.