It is simply not explanable that if John 6 is Jesus teaching of the true nature of the eucharist, that John does not mention the Lords Table in the Upper Room Discourse. The only gospel that does not mention the Lords Table is John.
Catholics have never had an even remotely cogent explanation for this contradiction; but they merely hand wave it away with a simple "the other gospels covered that already, John didnt need to."
John’s Gospel does not contain many of the things recorded in the Synoptics, including the Sermon on the Mount, the Transfiguration, the virgin birth, the Great Commission, and the Ascension. In fact, the only miracle outside of the Resurrection that appears in both the Synoptic gospels and John’s gospel is the feeding of the 5,000.
This doesn’t mean that John considered these things as unimportant at all. If John were, in fact, written much later than the other gospels, then perhaps John did not feel the need to replicate material that was already well established.
John writes for a very specific purpose, asserting that Jesus is the Christ, the Son of God, and that by believing we may have life in His name. (John 20:30-31) So, the material he selects is done so for the purpose of supporting that premise. All the miracles and all the teachings center around that premise. The Eucharist appears to have not fit into that selection criteria for him, since it doesn’t appear in the book.
And lastly, remember John 21:25.
“Jesus did many other things as well. If every one of them were written down, I suppose that even the whole world would not have room for the books that would be written”