Word for word? Really? Have you ever actually read these books?
They cover a lot of material, but that hardly amounts to word-for-word duplication.
I wouldn’t be quick to call it “pure conjecture.” The early chuch attributed this book to John, and the internal textual evidence which causes the popular view that John was indeed its author.
Poly, if we follow Renquist that would make the Gospels admissable to the question of whether the Gospel writers were culpable in an alleged conspiracy to present the Ressurection as historical fact. That is a separate issue to the question, “did the Ressurection happen”. In fact, given the secondary nature of the source material, it is not even necessarily to indict the Gospel writers as culpable in an alleged conspiracy.