The gospels being anonymous can be seen as moot if you see Papias and other early witnesses as generally reliable in creating a broad picture in the eyewitness testimony that is embedded in the gospels, not that all of what the early witnesses to the gospels had to say is accurate. John also probably got it's title when the appendix was added onto the gospel around 100CE or so and claims, by way of an editor, that at least some of the material in that gospel written by an eyewitness.
24 This is the disciple who is testifying to these things and has written them, and we know that his testimony is true. (John 21:24)
Anyway, in regards to the epistles, this is an over generalization per excellence.
This specific catholic epistle has much better prospects for authenticity as opposed to, say, 2 Peter and the Pastorals. Luke Timothy John in his commentary on p. 118-120 holds to the opinion that authenticity is reasonable, and an early date, contemporary with Paul's writing:
(Luke Timothy John, Anchor Yale Bible Commentaries, James, p. 118-120)
First, it can be accounted as a miracle that these two small little epistles and their fairly insignificant contents were preserved at all (Hengel, The Johannine Question, p. 26).
We know of a Elder (or presbyter) John figure who lived to the time of Papias' writing (95-110CE). Papias:
But I shall not be unwilling to put down, along with my interpretations, whatsoever instructions I received with care at any time from the elders...If, then, any one who had attended on the elders came, I asked minutely after their sayings,--what Andrew or Peter said, or what was said by Philip, or by Thomas, or by James, or by John, or by Matthew, or by any other of the Lord's disciples: which things Aristion and the presbyter John, the disciples of the Lord, say. For I imagined that what was to be got from books was not so profitable to me as what came from the living and abiding voice.
Notice the difference between the the members of the 12 said, and what the Elder John and Aristion, disciples of the Lord, still say.
And what do you know? Some of the Johannine corpus was written by someone who went by "the Elder"
2 John 1:1
1 The elder to the elect lady and her children, whom I love in the truth, and not only I but also all who know the truth
3 John 1:1
1 The elder to the beloved Gaius, whom I love in truth.
Papias is dated to 95-110CE for some the following reasons:
(Yarbrough, Robert W. (Jun 1983). "[The Date of Papias: A Reassessment" (PDF)(https://www.etsjets.org/files/JETS-PDFs/26/26-2/26-2-pp181-191_JETS.pdf): 181–191)
The ramifications of this may impact 1 John, the Gospel of John, and the book of Revelation as well.