But whence did the patriarchs get this collective authority? Universal authority in the Church can only be exercised by either the pope or the entire college of bishops. Even if they are in agreement the patriarchs only have authority over their own patriarchies; they have no canonical authority to act as a senate of the Church.
But even by your own logic the validity of the excommunication by Constantinople fails. If the Council of Florence can be rejected because it was not accepted by the Laos tou Theou in the East then Chalcedon must rejected because it was not accepted by the Laos tou Theou of Egypt and thus the legitimate Patriarch of Alexandria would be the Coptic patriarch. Thus at the time of Cyril VI's excommunication by Jeremias III of Constantinople only two (Constantinople and Jerusalem [and even the legitimacy of Orthodox Patriarch of Jerusalem is questionable]) of the five historical patriarchs (Rome, Constantinople, Antioch, Alexandria, and Jerusalem) concurred in the act.
“Universal authority in the Church can only be exercised by either the pope or the entire college of bishops.”
Not so far as we are concerned. Indeed, it is just that opinion, among others, which prevents a reunion of Rome with the rest of The Church.
“Even if they are in agreement the patriarchs only have authority over their own patriarchies; they have no canonical authority to act as a senate of the Church.”
Not so far as we are concerned. The Patriarchs can and have acted as a Synod with the EP as primus. The most recent example being the removal of Irenaeus.
“If the Council of Florence can be rejected because it was not accepted by the Laos tou Theou in the East then Chalcedon must rejected because it was not accepted by the Laos tou Theou of Egypt and thus the legitimate Patriarch of Alexandria would be the Coptic patriarch.”
That doesn’t follow at all, so far as I can see. And By the excommunication of Cyril VI, Rome’s opinion, it being in schism so far as we were concerned, was of no consequence.
This all started with the comment that the Maronite cardinal is the “Patriarch of Antioch”. He is not the Patriarch of Antioch in any traditional sense of the word. He is not the successor of any member of the Pentarchy. He is the Patriarch of Antioch for the Maronites but only for the Maronites. I say this, btw, with the greatest respect and admiration for the personal qualities of +Nasrallah.