These are futile arguments that give academicians something to publish without really saying anything new. This is no different than overpaid astronomers who get to play with multimillion dollar telescopes and postulate time-space warps.
None of this really does anything for the world. It doesn't cure hunger; it doesn't bring peace; it doesn't give mercy and compassion; it doesn't justify; it doesn't cure...In other words, its not God's work, it's not using our talents for the betterment of life.
The oldest fragment copy of a copy of a copy of the Gospels happen to be a few pages of John 1, from about 105 AD. It is unsigned. The caption Κατα Ιωαννην (According to John) was added in copies found in the latter half of the second century.
The Gospel of John also differs radically from the Synoptic Gospels, reflecting the belief of Christianity at the end of the first century, emphasizing Christ's divinity as opposed to His humanity of the earlier three Gospels.
His account of the timing of Christ's death and resurrection, as well as his theology, reflects a different era and a clear post-Jamnia state of Christianity as a separate religion. None of this could have been a historical account of early Christianity.
But, in the final analysis, it really makes no difference if any of the books of the Bible were really written by the people we believe they were written by. Isaiah, for instance, reflects three different authors and three different eras, making it impossible to be the the product of one single author.
The Church has consistently and from as early as we can tell followed the writings we now attribute to the New Testament. Of the four Gospels only two were written by alleged Apostolic eyewitnesses, Matthew and John. Mark, whose work is heavily copied by both Matthew and Luke, was not an eyewitness (and neither was Luke). And the Gospels of Matthew and John are like night and day.
But the Church found these to be inspired and reflecting the faith Christ delivered to his followers. It is the message of the Gospels that serves as the foundation of the Church and not the authors' names.
Early Church fathers never gave any account of authorship. The earliest Church (in the East) even tried to used an alamgamted Gospel, a conflation of all four into one. Some, such as St. Justin Martyr, speak only of "apostolic memoirs." (c 150 AD). It is not until Irenaeus at the vend of the 2nd centiry that we begin to see references made to Apostolic authorship.
Mark Shea's appeal to Saints Polycarp and Ignatius is also not a bulletproof "proof." We really don't know much about Polycarp and under which John was he instructed. Many of Ignatius' writings later on turned out to be latter-day forgeries.
The fact is that there is no solid proof that anything in the bible is true, or that the authors are those we believe they are. The Bible is a book that requires pre-existant faith in order to be profitable. No different than any other worldly writing considered sacred.
Let us not forget that even the heretics use the Bible to "prove" their heresies!
I don't buy 99% of the arguments of "textual criticism" because it almost always comes down to limited knowledge (later proven wrong, as has happened time and again down through the last couple centuries when it comes to textual criticism, or "higher criticism", by the so-called "experts"), incomplete knowledge, or simply "because we know the supernatural isn't possible, prophecy can't be real" (the real argument against Daniel's authorship and dating, for instance, even though the argument is absurd on its face for reasons too detailed to go into here).
Isaiah 53 was believed to be the work of later Christian scribes - interlopers - until the Dead Sea Scrolls were discovered...Oops! There was Isaiah 53, exactly as the modern Bible has it. DOH!