While I would not argue that a "good upbringing" (hence ability to do all the tribal signaling) is a major contributor to success, I would contend that claiming that most founders have these advantages is over-reaching. (Esp. given that most start-ups fail)

Coming from a remote Wyoming ranching childhood, I will claim that signalling can be learned, and that most if not all customers, VCs and bankers I might talk to are shocked to learn that I was not brought up just like them.

It's no different than lawyers or doctors, though. Every group has tribal signaling to help them identify if a person is in or out of their group. Learn to speak the language. Heck, even poor people (like me!) can do that.