That is JUST ridiculous.
John was ONE of the TWELVE apostles that will JUDGE the TWELVE tribes of ISRAEL. Why, exactly, would his letters be addressed to an audience that was predominately Gentiles?
Just ridiculous. Just a crazy fantasy of knowledge on your part.
For one, John's letters are not addressed to Jews so saying they were is an assumption based on a presupposition. Their content is not about Jewish issues: the Judaizers, the festivals, the Messianic Kingdom, prophecies. Instead, they address Docetism which was not a Jewish heresy but one that arose as an amalgam of Christianity, Greek philosophy and mysticism. Although the writer has a Semitic way of expressing himself the themes are simple, universal and do not require a Jewish background to understand.
Historically the letters of John were written in the last decade of the First Century when John was living in Ephesus. This was according to Irenaeus who was a student of Polycarp who was a student of John himself. The Early Church fathers report that John's ministry was centered in Asia Minor unless you think this was a fantasy of theirs.
The Churches in the cities of Asia Minor at that time were predominantly Gentile, not Jewish. There were a number of reasons for this. For one, the Roman's at he time of Nero began to differentiate between Christians and Jews so that later Jews actually joined in the persecution of Christians. This widened the division between Jews and Gentile Christians. Also, the base of operations for the Jewish mission in Jerusalem had been devastated along with the destruction of the temple and the martyrdom of the main leader of it, James the brother of Jesus. All of these factors contributed to the loss of Jewish membership in the Church.
John, having lived through all this became an important leader among gentile Christians, which comports with the fact that he was used to write letters to the seven Churches of Asia Minor in Revelation. John's trainee Polycarp was the presiding Elder in the Church of Smyrna mentioned in the Revelation. So you see, things were much different in the last part of the century than they had been some thirty years before when James, Peter and Paul were still alive.
These are facts of history that are accessible to anyone. Are we to believe that the Early Church Fathers falsified their accounts when they had no motive to do so or is it more likely that some proponents of MAD have concocted a pseudo-history to support their narrative when they do have a motive to do so? Personally I prefer to think that they were so centered on the text of the Bible that they did not carefully investigate their own claims.
In fact, the Twelve were never
prohibited from going to the nations. The "Jews-first" protocol ended but was never steadfastly adhered to. Besides in the Great Commission Jesus commanded to go. What history we know indicates that they went to places far away from Israel to Gentiles. The idea that they always ministered solely to Jews is what is a myth. None of this affects the fact that they will judge the twelve tribes of Israel in the Messianic kingdom