"Although the Jews hold that the oral tradition (Law) developed parallel to the written one, there is no evidence of a written one before 500 BC."
Only if you believe that the references within the Old Testament itself to written books of the law are lies. Right off the top of my head, there is the finding of the book of the law during the reign of the King Josiah -- which, I am certain, was several centuries before 700 B.C. There are others.
Furthermore, Christ speaks clearly of Moses as the giver of the books of the law. His appearing with Christ at the Transfiguration emphasizes this.
Christ furthermore refers specifically to both David and Solomon as historical figures. He specifically refers to Psalms as having come from David, as do the Apostles elsewhere in the NT.
Christ speaks of Abraham, Isaac, and Jacob as historical figures, and the Apostles treat the stories of them and the Exodus, etc. as being literally true.
I could go on.
For any Christian to accept the things from the Israeli "scholars" that you quote (which I don't believe you do), he would have to accept that Christ and the Apostles didn't know what they were talking about, or that they were lying.
So I don't think that your post is a particularly effective way of convincing FK about oral tradition. :-)
The overall point, though, is true: all Scripture was at one point unwritten oral tradition. They did not appear magically at the end of someone's pen.
What grounds Orthodoxy is the fact that we believe that oral tradition was and is part of the continuing presence of the Holy Spirit in the Church, and is not just an imperfect memory of the teachings of Christ and the Apostles.
It means that many parts of that tradition that weren't written down as Scripture continued to be passed down within the Church, some of which were later written down, but not treated in the same way as Scripture. Most importantly, it means that the Church's understanding of the Scriptures -- Old and New Testament alike -- carried on as a living tradition that continues to this very day.
One of our big problems with the Reformation approach to Scripture is that it cut itself off from this tradition, and attempted to go it alone in the interpretation of Scripture. Absent that tradition, there are myriads of different and mutually exclusive Protestant readings of the Scriptures.
I am simply stating what is known. As to whether the Israeli scholars are "scholars" or not is not mine to determine, nor ours to question simply because we don't like what their findings suggest. Sripture is an expression of God's revelation and is a testament of faith. It matters little if it is historically, or physicially accurate -- as long as it is spiritually accurate.
My older daughter, who knew God at the age of 10, but attended an Evangelical school, said about dinosaurs: "the devil planted those bones for us to find and be deceived," she said. "Dinosaurs never did exist." Oh, I see!
I think the hesychast Fathers unlocked the mysery of faith, namely that prayer is at the core of knowing, and reaching God and not academics. And while they studied the Scripture fervently, they leave no doubt that faith moves one to pray and that prayer alone humbles us and brings us to God by His mercy.
As another blessed Father says "...faith is that which completes our argument." St. Gregory Nazianzen (Third theological Oration no. 21) Everything else is mental exercise.