Miyabi,
It is true that the gnostics were written in a cluster near one another and the majority of scholarship agrees that this was at least as late and the 4'th century.
To find a majority of scholars who agree that the works of the New Testament were written that late you would have to take a sample that did not include those who are members of various Christian sects. I'm not arguing about faith. But you have to find skeptics and crack-pots who have a vested interest in disproving any divine origin in order to find any large number who are willing to go out on a limb and claim definitively that any of the NT texts were not written by the men who's names were applied.
The issue arises because we don't have a single manuscript, meaning something written in the hand of the writer. We have only copies of copies because the media themselves were subject to wear and tear. Also because the letters (in the case of the epistles) were circulated and possibly even collected into anthologies. Instead redaction and hermeneutics have to be applied, along with archeology to determine dates relative to verifiable events, language patterns and quirks of the author.
You have to be a pretty dishonest scientist to say that the because of the carbon dating of the media on our oldest copy is X therefore the document is only as old as X. So instead, we get a lot of vague claims most of which are pretty specious and which come from wild-eyed extremists with an axe to grind. It's been vogue to bash the Bible, Christians and Jews for so long that people have begun to accept hate speech as science and bias as scholarship.
But when you allow ALL the players at the table (i.e. don't exclude those who happen to believe the bible's contents) in the debate about the language science. The TREND is toward the men who are named as author being the men who were the writer's or at most the men who dictated the content to an amanuensis. Granted they probably used a document which has been lost as a reference work, but that doesn't precluded the idea that men facing death may have written or dictated their accounts in order to preserve their faith.
My Advisor was a Harvard Don who would have sneered at the idea of the gnotics being contemporary with the four NT.
But we've gone pretty far afield from discussion of the Level titles. Can't wait to see what I get next.