Brother, in session III of Chalcedon Leo was addressed to, by Eusebius, as: “The most holy and beloved-of-God ecumenical archbishop and patriarch of great Rome Leo…”
newadvent.org/fathers/3811.htm
Throughout that Council, Leo is the only bishop called “most holy”, “most blessed”, “apostolic”, etc.
It is the ancient Christian religion; not “the most ancient”, or “an ancient”, but
the ancient, as God is not the most ancient religious idea of men, but is
The Ancient of Days.
However, if we examine the minutes of Ephesus II, we’ll see that Dioscoros is called, “our most holy father Dioscorus, ecumenical archbishop of the great city of Alexandria.” The only times I can see in the council where Pope Leo is called ecumenical archbishop are the appeals written by the plaintiffs who wished to have Ephesus II overturned. It would, of course, be to their benefit to use such flowery language when addressing pope Leo. (now unless I am missing something, the council never refers to pope Leo in such a way, just the plaintiffs)
This usage however, has nothing to do with the official title, “Ecumenical Patriarch,” but rather only has to do with the plaintiffs calling pope Leo the “Universal Patriarch.” The actual title Ecumenical Patriarch comes by way of the Patriarch of Constantinople’s connection with the city of Constantinople, which eventually began to be known as the Ecumenical City. It was only natural that the patriarch residing in the Ecumenical City should become known officially as the Ecumenical Patriarch. It has a completely different connotation from how the word Ecumenical is used in the council of Chalcedon.
Pope Leo was also not the only one to be known as most holy at the council. The problem is that what you linked is a highly abridged edition. Here are a few examples of other bishops being called most holy from a complete translation of the acts:
From the first session:
“85. When it had been received, John presbyter and protonotary said: ‘Another pious decree was sent to our most holy and God-beloved Archbishop Dioscorus, which we have in our hands for the pleasure of your holiness.’”
And here are some readings from the minutes of Ephesus II in which Dioscoros was called most holy:
“200. Stephen bishop of Ephesus said: ‘Since the proposal of our most holy and God-beloved father and Archbishop Dioscorus is a fair one, let it be put into effect.’”
“201. Cyrus bishop of Aphrodisias said: ‘The proposal of the most Godbeloved and holy Archbishop Dioscorus for the reading of the proceedings in the case in the imperial city is both fair and fitting.’”
“213. Atticus bishop of Nicopolis in Epirus Vetus said: ‘Since the proposal of our most holy Archbishop Dioscorus is fitting, let it be put into effect and the minutes be read to all the most holy council to give more accurate information about the points under examination.’”
“215. Uranius bishop of Hemerium in the province of Osrhoene, with Eulogius presbyter of Edessa acting as interpreter, said: ‘The most holy and religious Archbishop Dioscorus has made a fitting proposal that the proceedings at all-fortunate Constantinople about the case in question should first be read.’”
As you know, Dioscoros was later deposed by the council for failing to show up after being summoned three times.
Here they are also in the first session, calling the reposed Archbishop Flavian ‘most holy’:
“293. Athanasius the most devout bishop of Busiris of Tripolis in Egypt said: ‘The most holy Bishop Flavian followed the letters of the most sacred Cyril, and expounded the faith well.’”
“294. Auxonius the most devout bishop of Sebennytus said: ‘The most holy and devout Bishop Flavian thought and spoke in harmony with the teaching of Cyril as contained in the letters of the most sacred Cyril that have been read.’”
There are plenty of other examples of even minor bishops being called “most holy,” “most blessed,” “most God-beloved,” “most devout,” or “most religious” throughout the acts of Chalcedon, so I’m not sure if this is a good argument. The honorific language being applied to pope Leo was pretty standard for all people of high ranking during the time period.