“In EY there is an unsettled dispute as to who rules the roost.”
There is NO question as to the original minhag of America: The Spanish/Portuguese/Dutch Sefardic nusach. There is not a single orthodox Ashkenazic synagogue in the US that is less than a century NEWER than Shearith Israel in Manhattan and Mikveh Israel in Philadelphia. It is no wonder that every single Ashkenazic congregation founded in America prior to 1850 either died or became non-Orthodox; to violate the well-established minhag hamakom was itself a serious halachic issue. Note that both Shearith Israel and Mikveh Israel remain orthodox to this day.