Some people could argue the appearance of the expression “first among equals” shows a phenomenon similar to the evolution of dogma.
E.g., the words and expressions “Holy Trinity”, 'purgatory", “papal infallibility”, and “Immaculate Conception” cannot be found as such in the Bible, and some of these expressions (e.g. “papal infallibility” and “Immaculate Conception”) cannot be found in the Early Church Fathers.
Yet, I will point out that the ECF (e.g. St. Ephrem of Syria, 4th century) did write about Mary’s sinlessness, and St. John Chrysostom’s Divine Liturgy (composed in early 5th c.) does contain one of these hymns praising Mary as being incomparably more glorious than the Cherubim, infinitely more exalted than the Seraphim. So, if someone would try to say, “the ECF do not use the expression ‘Immaculate Conception’”, we could immediately send that person to patristic writings that form the foundation of the dogma, and more than that, show that the Book of Genesis prophesies about a Woman whose seed will crush the serpent’s head, and there’s the Woman clothed with the sun and 12 stars in the Book of Revelation. In short, the whole idea of “Immaculate conception” is based on certain passages in the Old Testament, New Testament, and the writings of the ECF.
We can make a similar argument regarding “papal infallibility” - there’s a historical parallel here of God leading Israel through Moses in the Old Testament, there are the famous Petrine passages (Mt 16:18, Lk 22:31, Jn 21:15) in the New Testament, and a bunch of patristic writings starting with St. Clement in the 1st century, St. Ignatius of Antioch and St. Irenaeus in the second c., and going on and on and on, forming the basis of the idea of “papal infallibility” and “papal universal and ordinary jurisdiction”.
But someone who believes that the Pope is “first among equals”, please show me the basis of your idea. Because, if the idea existed in the ancient Roman Empire as applied to the emperor, that doesn’t cut it. That’s a secular idea. You must rather show me where in the Old Testament do we have a governing body without a single leader. Show me where in the New Testament does Jesus Christ give an equal authority to the rest of the Apostles as he gives to Peter. And, if you can’t find the exact expression “first among equals” in the ECF’s writings, show me where did the ECF teach that Peter did not have a real leader’s authority, only some sort of primacy of honor.
In my mind, the case against “first among equals” is even stronger when we try to search for Old Testament foundations, New Testament foundations, and patristic writings, Early Church documents supporting the idea. What I’ve read so far does not support this concept of the Pope being a “first among equals”.