It seems like the council of Nicea formalised the already existing custom of the borders of the ancient Patriarchates of Alexandria, Rome and Antioch. Constantinople and Jerusalem was added later if I'm correct?
I doubt you will find many people here to be overly enthusiastic about your "find" that the Patriarchates are equal. We are after all Orthodox and this is how we have understood the Church to function since the beginning. (I'm sorry to be teasing you
I must congratulate you on finding this on your own though. Most people are not that eager to check out the sources for themselves.