"Are the the authors making the case that the modern concept of nationhood status confers upon Indigenous peoples a separate set of rights based upon their own laws and legal traditions, and that the SCC has no status in Indigenous affairs...?"
That is exactly how I read the authors case.
In fact this could be taken a step further, that what we presently call the Government of Canada including the Supreme Court does not have a legal right to exist. And laws and legal traditions of First Nations control Canada.