There's not even any clear evidence that the Gospel of John and the Johannine epistles were written by the same man, is there?
Critical scholarship based on textual analysis is divided.
A majority think the gospel and the epistles were products of a Johannine school centered on the Apostle John, with John himself being the editor of the gospel thus making him the author in the same sense that Cranmer could be viewed as the author of
The Book of Common Prayer.
Many think John wrote the the first epistle himself, with doubts coming mainly from those who think its content points to a date after John's death. I can see it being a work written at the very end of his life when John was likely the last Apostle still living and expected that Jesus would soon come before he could die.
The other two letters are so inconsequential, its hard to know who wrote them or when, tho most think those two share common authorship based on textual analysis. I think it likely given their content and that they were preserved is that what happened was John told his secretary to write a brief note telling the recipient that John planned to come visit them and why. So in that sense they're letters of John the Apostle.
It's not like the Apocalypse of John, where the style is so different from the remainder of the Johannine literature that few critical scholars think it shares authorship with the rest of the Johannine corpus, and I share those doubts. For that matter, I have serious doubts that the Apocalypse of John the Servant should even be part of the canon, but I haven't come to a conclusion.
Incidentally, as long as we're talking about Revelation, let me mention one idea I've had for who the twenty four elders are in the book. Given the highly symbolic language of apocalyptic language in general, it's not even certain that they represent people. I think a good case can be made for them representing the twenty-four books of the Jewish cannon and thus symbolizing the common assertion that
everything in the Old Testament points to Jesus if you only know how to read it. (Some books considered separate books in Christian labeling are part of one book in the Jewish canon, with the most extreme example being that the twelve Minor prophets are in Judaism one book instead of twelve.)