You have been misinformed. We have none of the original manuscripts, but we have remnants of copies of Matthew found in Egypt that date to 80 AD at the latest, and some claim that there are some that date to the 50's AD. Also, John specifically claimed he was writing as an eyewitness, John 21:24-25.
Higher Criticism was developed by liberal "scholars", many of whom deny miracles, prophecy and the resurrection from the outset, and their "scholarship" is a product of those premises.
He can claim that if he likes, but that doesn't make it true.
The earliest writings are the Epistles, many of which are pseudepigraphic. The Gospels come from around 90 AD.
http://www.asia.si.edu/exhibitions/online/ITB/html/earliestScriptures.htm
http://www.bible.ca/ef/topical-the-earliest-new-testament-manuscripts.htm
They are NOT comtemporaneous manuscripts, thus not eyewitness reports. They have been subject to telling and retelling before being written down, with the propensity for distortion that that entails.
Furthermore, since there are literally thousands of copies, all handwritten, there are numerous transcription errors over the years, as well as copies with material either added or deleted. While we may never be able to reproduce the original text, comparison and contrast will get us just about as close as we can get.
It’s amazing how much the version we have has been altered even from the earliest versions we have, which are not originals and therefore probably contained alterations themselves.
I tend to think that because of the Destruction of Jerusalem in AD 70, that those who believe in earlier dates for most (all?) of the NT are correct.
Otherwise, the gospel writers would make a VERY big deal out of Jesus’ prediction of Jerusalem’s fall coming true.
Makes sense to me, anyway.
Further, we have some manuscripts which date to the 50's which cannot be attributed but which recount some of the events described in the gospels.
The criticisms about the dating also does not sound as critical when you observe that the manuscripts recount events that occurred in the last half of the third decade (25-30 AD).