"If there was a historical Jesus, then he was nothing like the Gospels". And that's fine. A historical Jesus, if one existed, almost certainly wasn't like the Gospel Jesus. Then:
"Early Christians like Paul don't refer to Gospel-like events when talking about Jesus, so the lack of Gospel-like details when talking about a Jesus (who was nothing like the figure in the Gospels in the first place) is evidence against that Jesus."
Both statements can't be true!
There's much more to mythicism than just that, of course. And if you are arguing against someone who thinks that a historical Jesus was like the Gospel Jesus, then it's fair enough to ask why Paul, say, doesn't mention Gospel-like details. But that isn't the only HJ in town.
What I thought I'd do is explain why I think some kind of historical Jesus is the best explanation for what we see in the earliest layer of Christian texts (letters by Paul and gMark) and who that historical Jesus probably was.
I'll start by saying that to me, Paul believed that Jesus was a Jewish man who lived in Paul's recent past. If you believe that's not true -- that, say, Paul believed Jesus took on a body of flesh in other space and was crucified by demons -- then fair enough, we can agree to disagree and argue over the details separately.
Who was that Jesus? Paul describes him as humble-minded, "obedient unto death", "who knew no sin" and because of that was declared Son of God by resurrection. "Obedient unto death" implies that, before death, he was obedient(!) More on that later.
People had visions of the resurrected Jesus and for some reason thought he was the Christ, either before or after death. But if he was Christ (the argument goes), then he'd have to conform to Scriptures. We see this view quite clearly in Acts of the Apostles. And so stories about that Scriptures-conforming Christ figure started to appear. At some point, the author of gMark collects them, probably adds some more him/herself, and probably adds in stories about Paul and other apostles and makes them into stories and sayings about Jesus. Other writers started doing the same.
Meanwhile, the new god Jesus starts being used by people to do healings, exorcise demons, etc. We suddenly see magicians like Simon Magus, Menander, Basilides popping up around this time. Independent religious entrepreneurs like Paul and on all sides -- Jews and pagans -- start invoking the heavenly powers of Jesus, leading to the growth and popularity of the movement. There was a riotous diversity at that time: mystery religions, gnostic, anything that could use this new heavenly power. Some tried to align within Judaism (Ebionites), some outside Judaism (Marcion), some in between.
Eventually one part of the movement, the proto-orthodox, gained enough power to enforce orthodoxy. It tried to become respectable by showing how much Christianity aligned with Greek philosophers and so Christianity was retro-fitted. Part of that was using the Gospels to portray Jesus as more like a Greek philosopher. At that point, the Gospels started to become authoritative and the life of Jesus took on a significance that it didn't have until then. Previously it was his death and resurrection to heaven that was important, not his life.
So, who was that historical Jesus? Paul describes him as humble, coming as a servant, obedient unto death. We see this theme in other early literature:
According to Justin Martyr, around 150CE:
http://www.earlychristianwritings.com/t ... rypho.html
[Justin replies] But since I have certainly proved that this man is the Christ of God, whoever He be, even if I do not prove that He pre-existed, and submitted to be born a man of like passions with us, having a body, according to the Father's will; in this last matter alone is it just to say that I have erred, and not to deny that He is the Christ, though it should appear that He was born man of men, and [nothing more] is proved [than this], that He has become Christ by election. For there are some, my friends," I said, "of our race, who admit that He is Christ, while holding Him to be man of men
And Trypho said, "Those who affirm him to have been a man, and to have been anointed by election, and then to have become Christ, appear to me to speak more plausibly than you who hold those opinions which you express. For we all expect that Christ will be a man [born] of men, and that Elijah when he comes will anoint him. But if this man appear to be Christ, he must certainly be known as man [born] of men; but from the circumstance that Elijah has not yet come, I infer that this man is not He [the Christ]."
Also in Hebrews:
8 though He was a Son, yet He learned obedience by the things which He suffered.
9 And having been perfected, He became the author of eternal salvation to all who obey Him,
Also in 1 Peter:
22 Who did no sin, neither was guile found in his mouth...
In Hippolytus of Rome, Refutation of All Heresies 7.22
It doesn't tell us much about a historical Jesus, to the point he might as well not have existed. But so what? We have what we have. The insistence that a historical Jesus has to in some way be like the Gospel Jesus is a strawman (unless arguing against someone who is actually making that claim).
So, speculating: how did Jesus' obedience lead to death? Here I turn to the Gospels. Not because I regard their content as true, obviously, but because they are really all we have. I think the story of Jesus objecting to practices at the Temple is as plausible as any. He was complaining that the Jewish elite were not adhering to the Law and therefore not adhering to God in some way. At a time when Cancel Culture involved crucifixion, he was cancelled. It fits with the theme of obedience "unto death".
Epiphanius, writing in the Fourth Century CE, refers to heretics he calls "the Herodians". These were people who believed that the dual role of King and High Priest ended with the death of Alexander Jannaeus around 70 BCE, and that ending conformed with the prophecy signifying the coming of the Christ. This pointed to King Herod the Great as being Christ.
I speculate that the ending of the dual role of King and High Priest started up groups like the Herodians that were expecting a Christ figure to come soon. These were the Churches in Christ and Churches of God that Paul was persecuting. Perhaps Jesus was part of one of those groups (I thank Earl Doherty for that idea, which comes out of his analysis of Q). For some reason Jesus was assigned the role of Christ, either before or after death, it's impossible to say.
Anyway, that last part aside: I think my theory is consistent with what we see in Paul and other early epistles. Early Christians were more interested in Jesus' death than in his life. The idea of a "newspaper reporter's Jesus" -- one where Jesus was such an important figure during life that he would have been noticed even if he wasn't thought to have been resurrected -- is a strawman. But lots of Christian scholars and some mythicists just can't let it go. Please stop using that strawman!