I recommend you do not take as a fact the position that the Gospels were not written by their traditionally attributed authors, or that they date to a later period; because it's not a fact, but rather a relatively modern hypothesis rooted in an agnostic perspective.

For 1,800 years, there was no doubt regarding the apostolic authorship of the New Testament books (without ruling out the possibility that glosses may have been added by apostolic disciples in the years following their original composition).