I’ve never been able to quite wrap my mind around this argument. If anything, just based on textual style, there is more of an argument to be made for the Apostle John to have written the book of Revelation. The original Greek text is littered with spelling and grammatical errors, some of them real howlers. Word order and sentence structure indicate that Greek could not have been the native language of whoever wrote the text. This would be consistent at least with the theory that John the Apostle could have written it, given he was most likely illiterate in any language, and if he ever learned Greek, he would not have done so until later in life. Of course, that’s not positive evidence for his authorship, it’s just consistency.

Whoever wrote the Gospel of John on the other hand, wrote in fairly elegant Greek that scholars say sounds native or at least highly educated. It’s the sort of beautiful Greek scholars say would be very difficult to acquire casually, especially for a man not educated in Greek as a child or youth.

This doesn’t argue against the Apostle John collaborating with a literate Greek speaker to write the Gospel, but it calls his authorship into serious question.

I just think of myself, a serious Francophile who started learning French in my thirties. While my command of the language is excellent and I have no difficulty understanding, speaking, or writing, I could never produce a work in French that scholars would call literary or beautiful without at least mentioning that it doesn’t sound natively French.

Just food for thought.