I was unfamiliar with the idea of the scapegoat also being a “truth teller” in a narcissistic family. The truth teller might also be called a witness; it’s the child that knows something is not right and thus threatens the vulnerable narcissist. Many if not most traditional cultures have very large narcissistic components. Their moral strictures, religions, duties, values, manners, etc. almost all contain elements of narcissism. So there is an important historical dimension to this diagnosis.
Aspects of Buddhism as it is traditionally practiced even today can also be seen as being narcissistic or fostering narcissism. Same for all the Abrahamic religions, Confucianism, Aztec beliefs and so on across the globe. Just as consciousness is fundamental to our human reality so are the many ways of interpreting it, almost all of which historically have tended toward narcissistic systems.
Truth tellers typically are most likely to escape the web of the narcissistic family even though their role in it was to be the most despised, the scapegoat. Sometimes I see the Buddha as a truth teller who freed himself from his father’s make-believe world despite the power and luxury it offered. He was more a golden child I suppose than a scapegoat. In this vein, Jesus can be seen as an outcast black sheep who was tortured and grossly humiliated. Both embody the hardship of earning freedom from delusion.