The tendency to not be attracted to people you grew up with is an innate thing, but it's not absolute, relationships do sometimes develop between childhood friends, for example. And I don't feel confident saying that for example tribal societies, or even the large multi-generational households that were more the norm before the Industrial Revolution, always necessarily had the same power dynamics of modern day families, since the nuclear family is a relatively recent thing. But I do agree with you in the context of the modern day.