I’m not arguing anything.
Just speculating.
Was John the Evangelist the young aristocratic priest who was taken with both Jesus and John the Baptist? Was he the one who provided the room for the Last Supper? Provided a haven for the Christians in the weeks after the Crucifixion? Followed Jesus back to Jerusalem after he was arrested by the mob? Let Peter stay in the courtyard of Caiaphas? Was present when Jesus was crucified?
I think you’re basing too much speculation on a single source that claimed John was a priest - Polycrates, bishop of Ephesus (189-98).
In Asia also great lights have fallen asleep, which shall rise again on the last day, at the coming of the Lord, when he shall come with glory from heaven and shall seek out all the saints. Among these are Philip, one of the twelve apostles, who sleeps in Hierapolis, and his two aged virgin daughters, and another daughter who lived in the Holy Spirit and now rests at Ephesus; and moreover John, who was both a witness (
martys) and a teacher, who reclined upon the bosom of the Lord, and being a priest wore the sacerdotal plate (
petalon). He also sleeps at Ephesus.
To be fair, we don’t know just in what sense Polycrates considered John to be a priest here. Does it refer to the
Jewish priesthood or the
Christian priesthood? Does his reference to the ‘sacerdotal plate’ (sometimes translated as ‘mitre’;
petalon is the same word used in the Septuagint to refer to the golden plate in the high priest’s headgear; Exodus 28:32/36) mean that he thought John was actually the high priest? More importantly, is this supposed to be historical or metaphorical? (It doesn’t really help here that Polycrates confuses Philip the Evangelist of Acts with the apostle.)
You also have to consider the context in which Polycrates makes this claim. He was writing to the bishop of Rome defending the practice in his area of celebrating Easter on the same day as the Jewish 14th of Nisan - no matter what day of the week it fell (Quartodecimanism). His claim of John wearing the high priestly headgear (which could symbolize the apostolic authority John had) could be read as his trying to enhance his own position regarding his celebration of Easter on 14 Nisan by invoking the authority of John.
Some even say that the ‘John was a (high) priest’ idea may ultimately come from a Christian interpretation of a passage in Acts (4:5-6), which speaks of a John among the high priestly family: “On the next day their rulers and elders and scribes gathered together in Jerusalem, with Annas the high priest and Caiaphas
and John and Alexander, and all who were of the high-priestly family.” It was common Jewish and Christian exegesis to lump together people who share the same name into one figure. (Look at all the different Marys in the gospels; sometimes early Christians conflated many of these Marys together. Also the Zechariah who was murdered in the temple with Zechariah the father of John the Baptist.)
It’s true that John (the author of the gospel), if we are to identify him as the unnamed beloved disciple, does seem to have priestly connections or at least had some knowledge of the goings-on among the priesthood (he was known to the high priest, he seems to have knowledge of people like Nicodemus or Joseph of Arimathea, he mentions the high priest’s servant’s name and also the fact that one of those who questioned Peter was the servant’s kinsman, his account of Jesus’ trial before the high priest has more verisimilitude than the synoptic versions, etc.), but that’s really all we know. Anything else beyond that is speculation.
In Christian tradition, other people who are claimed to be high priests include the prophet Simeon (Luke 2:25-35 - this could have arisen due to the conflation of this Simeon with Simeon the son of Clopas, second bishop of Jerusalem and successor of James ‘brother’ of Jesus), John the Baptist’s father Zechariah, and James Jesus’ brother. But compared with these other three, the sources which refer to him in (high-)priestly terms are very few and sketchy.