In a justice system strongly inspired by common law, court decisions establish laws to the extent necessary to resolve the case before the court.
Obviously, the Supreme Court will make a slightly broader ruling. However, if we respect the philosophy of common law systems, we must still read the decision based on the question asked and the particular context of the question.
As you said, the particular context of the Nadon case is the protection of Quebec's representation on the Supreme Court. The court told us that a historic compromise was reached that helped establish the Supreme Court in 1875. Clearly, the authors of the 1982 Constitution still had this compromise in mind. Essentially, the text gives Quebec a right of veto with regard to its representation on the court.
This shows us the importance of paragraph 41(d). The Nadon decision must be read from this perspective. Obviously, the reasoning doesn't apply when we're no longer talking about Quebec's representation on the court.