So, did the apostle John write the book of John?
Despite alternative theories about the disciple whom Jesus loved, most evidence still points to the apostle John. The early church father Irenaeus wrote, “afterwards, John, the disciple of the Lord, who also had leaned upon His breast, did himself publish a gospel during his residence at Ephesus in Asia.” Irenaeus lived in the second century, and claimed to receive this information from John’s disciple, Polycarp
*The discovery of the Dead Sea Scrolls in Qumran marked a change in Johannine scholarship. Several of the hymns, presumed to come from a community of Essenes, contained the same sort of plays between opposites – light and dark, truth and lies – which are themes within the Gospel. Thus the hypothesis that the Gospel relied on Gnosticism fell out of favor. Many suggested further that John the Baptist himself belonged to an Essene community, and if John the Apostle had previously been a disciple of the Baptist, he would have been affected by that teaching.[citation needed]
The resulting revolution in Johannine scholarship was termed the new look by John A. T. Robinson, who coined the phrase in 1957 at Oxford. According to Robinson, this new information rendered the question of authorship a relative one. He considered a group of disciples around the aging John the Apostle who wrote down his memories, mixing them with theological speculation, a model that had been proposed as far back as Renan’s Vie de Jésus (“Life of Jesus,” 1863). The work of such scholars brought the consensus back to a Palestinian origin for the text, rather than the Hellenistic origin favored by the critics of the previous decades.*
Here is a unbiased source that sez it isnt settled:
In the end, the most likely scenario is that the Gospel of John was written by John son of Zebedee.
C*onclusion: I believe that John the apostle authored the Gospel by dictation. That is to say, John most likely provided the material to an amanuensis. The amanuensis documented the aged apostle’s words and added the addendum to the Fourth Gospel and the title “the disciple whom Jesus loved” in reference to the apostle. I think the evidence is quite strong for John the son of Zebedee authoring the Fourth Gospel. Claims to the contrary[4] bring more questions than answers. *
So, altho you may claim that there is much debate and the question is by no means settled, sure, you cant claim “the debate is pretty well settled” because it just simply isnt.