I would agree that the canonical Gospel of John in its current form – composed of a prologue, a Book of Signs, a Book of Glory, and an addendum – is a later compilation.

However, I do not believe that the Gospel of John suddenly sprung into existence in the later half of the first century, but rather pulled material from older (potentially heretical) written traditions along with later revisions, including those with gnostic influences as there’s hostility toward the archon of the world (John 12:31, John 16:11, John 14:30) which is a repeated theme among the historical list of heresies and also potentially Samaritan Christian influences as Jesus is declared to be the Prophet like onto Moses (John 6:14, John 7:40). The lack of a nativity story does match the theology of Cerinthus who believed that the human Jesus merged with the divine Christ at baptism.

Paul does note that other gospels were already in existence by the time of 2 Corinthians and that Apollos had generated written material of his own in 1 Corinthians.

“For if he who comes preaches another Jesus whom we have not preached, or you receive a different (Holy) Spirit which you have not received (from me), or a different gospel which you have not accepted (form me) – you may well put up with it!” (2 Corinthians 11:4)

“Now these things, brethren, I have figuratively transferred to myself and Apollos for your sakes, that you may learn in us not to think beyond what is written, that none of you may be puffed up on behalf of one against the other.” (1 Corinthians 4:6)

I suspect that a sect of Samaritan Christianity may have first declared Jesus to be the “I AM” as John 8:48 states “Do we not say rightly that You are a Samaritan and have a demon?”

In terms of potential candidates, I’d suspect ‘Dositheus’ – possibly Apollos.

““Such were Simon, the Magus of Samaria, and Dositheus, who was a native of the same place; since the former gave out that he was the Power of God that is called great, and the latter that he was the Son of God. Now Simonians are found nowhere throughout the world… The Dositheans… are completely extinguished” (Origen Contra Celsium 5.11). I find it peculiar that Origen (c. 185-253) never met a single Simonian or Dosithean at that early point in history, especially noting Simon’s vast success at finding converts among the Samaritans. I suspect both are literary constructs released by the Jewish Christians who could not name their opponents outright.

The author of the Gospel of Mark was arguably already aware of the existence of a competing sect of Christianity preaching a competing version of Jesus that referred to Him as the I AM when he wrote his gospel.

The written material in circulation at that early point in history was, arguably, not the final form of the Gospel of John, but more likely a proto-type from which the canonical Gospel of John siphoned material off of.

Either that or you can count Jesus as a prophet, or even the Prophet.

But those preaching would arguably have been written down over time, potentially by the time the Gospel of Mark was written. Transmission of religious thought tends to work far better when there is written material to back up claims. Competing sects of Christianity would have known that. Apollos is noted for having “written” (1 Corinthians 4:6) something that was causing Paul’s followers and Apollos’ followers to be “puffed up on behalf of one against the other.” (1 Corinthians 4:6)

There was clearly already “another Jesus whom we have not preached” (2 Corinthians 11:4) by the time 2 Corinthians was written, and based on the sheer number of first century heresies, more Jesuses definitely cropped up like mushrooms. The possibility remains open that a Samaritan someone was already preaching a Jesus who he (or she) declared to be the “I AM” by the time the Gospel of Mark was written.