The late Vilakuvelil Cherian Samuel (1912-1998), priest of the Malankara Orthodox Church and one of the leading Oriental Orthodox (Indian Orthodox) scholars of the 20th century, is quite plain in admitting that Pope St. Leo the Great expressed the theory of Papal supremacy in the 5th century. However, what I found surprising is that in the midst of making that point, he, as an Oriental Orthodox scholar (upholding the Council of Ephesus 431), admits that the very same claim to Papal supremacy was made in the presence of the Council of 431 by the legate of Pope St. Celestine, Philip. I find it interesting how, when Orthodox apologists, such as Ubi Petrus or others, have to deal with the clarity of Pope St. Leo, they do all that they can to tone down the import of the language. I've seen the very same thing done by Oriental Orthodox apologists, namely, when they try to tone down what Philip said at the Council of Ephesus (431) by Philip. Fr. Samuel did not play that game.

The Council of Constantinople 879, by itself, can only get you so far. As it stands, it affirms Papal supremacy based on the divine commission of Jesus Christ, something unanimously rejected by Eastern Orthodoxy for centuries, and it rejects the addition of any words to the Creed of 381, something the Catholic Church has done for centuries. Florence picked both of these matters up due to evidence unexamined at 879, namely, the unanimous Patristic support for the procession of the Holy Spirit from the Father and the Son. Mark of Ephesus knew that if the Latin Fathers taught the Filioque in the form of a choir, then the cause for the Greek separation is completely unjustified. Well, scholarship is pretty unanimous now that the Western Patristic heritage taught the substance of what was codified at Florence. The proof of this is that Mark of Ephesus spent not a single second trying to prove that the Latin Fathers were Photian in the post-Florentine anti-unionist literature. If the opportunity was there, he and others would have surely taken it. So the Greeks will have to try to turn to something else, such as purgatory, indulgences, divine simplicity, the beatific vision, or something else... because 879 only helps Catholics, and Florence's basic point on the Filioque was proven right.