So the one section on wiki breaks down the page as arguments in favor of authenticity, arguments of partial authenticity and arguments for complete forgery with respect to the "testimonium flavianum" which is within book 18.
But the reference to James brother of Jesus is in book 20 and wiki states the following:
Modern scholarship has almost universally acknowledged the authenticity of the reference to "the brother of Jesus, who was called Christ, whose name was James"
[13] (τὸν ἀδελφὸν Ἰησοῦ τοῦ λεγομένου Χριστοῦ, Ἰάκωβος ὄνομα αὐτῷ) and has rejected its being the result of later
Christian interpolation.
[14][98][1][15][18]
Then back in book 18 is reference to John the Baptist, which of course is another significant figure in the Bible, in which the wiki states the following:
In the
Antiquities of the Jews (
Book 18, Chapter 5, 2) Josephus refers to the imprisonment and death of
John the Baptist by order of
Herod Antipas, the ruler of
Galilee and
Perea.
[19][20] The context of this reference is the 36 AD defeat of Herod Antipas in his conflict with
Aretas IV of
Nabatea, which the Jews of the time attributed to misfortune brought about by Herod's unjust
execution of John.
[21][129][130]
Almost all modern scholars consider this passage to be authentic in its entirety, although a small number of authors have questioned it.
[19][131][132] Because the death of John also appears prominently in the Christian gospels, this passage is considered an important connection between the events Josephus recorded, the
chronology of the gospels and the dates for the
ministry of Jesus.
[19]
I think what this is all telling us, is that, people of this time, the first century, and at the time Jesus is claimed to have lived, are talking about Jesus. They're talking about John the Baptist, they're talking about James. Jewish historians like Josephus are talking about them, even Tacitus' book was only written some 20 years after the gospel of John, (and 50 after Mathew and luke) even as second hand sources, these guys are present in these series of events. The apostles and followers of Jesus were alive during this time and they're working up the new testament.
And while it sounds like the gospels may be the only 1st hand accounts of Jesus (Even though we don't know the names of specifically who wrote them)...realistically, im not sure that we ought to expect other sources beyond them. Jesus was basically a, according to the gospels, he was basically a rebel. He had no power, he didn't finance scribes to follow him around. It was just the poor and needy that largely followed him. And his apostles were just regular Joes, and fisherman. They werent particularly organized. So I'm not sure that we ought to expect much more from this beyond what we have in the gospels. They aren't exactly professional scribes.
And the second hand sources, all they can do is say, hey, these rebels called Christians are causing trouble. I didn't see Jesus crucified, but my sources say it happened (Tacitus who hates Christians and I can't imagine would listen to them), and right now, this guy by the name of John the Baptist has been executed (Josephus, alive at the time) and James who claims to be Jesus' brother, is also around (Josephus in another statement considered authentic). Which is all we might expect second hand accounts to say as well. Whether Josephus' spoke of Jesus beyond talking about his apostle brother James, or John the Baptist, seems to be disputed.
Personally, I think this is pretty convincing. Obviously nobody can really know for sure what was going on this time. But I think this is convincing in the sense that it suggests the christian movement got started and was rapidly moving for some reason. And...it was focused around a figure named Jesus.
I just think it's easier to suggest that there probably was a leader who caused these sequences of events to happen. Maybe it was a crazy person just like the Waco davidians leader. Maybe it was truly a divine man. Or maybe it was someone named Jesus who was somewhere in between.
But to say that there was no Jesus. I think that just sounds kind of odd. Did the Waco Davidians make up David? We know plenty of people in these times were trying to start movements like this. Seems feasible to me that a man (divine or not) named Jesus was probably real. Someone had to inspire people. Someone had to inspire John the Baptist. And James, brother of Jesus (allegedly).
And one last thing. The Gospels are exceptionally explicit in detail about Jesus. Who he was, what he said, where he went, how he acted, dates, when he was doing stuff during certain times of the year, who he spoke to etc. He went north to this city, then went east to this town, then went to this temple in that town, then went back south to the other city. Etc. The Gospels are very explicit.
It just seems all too coincidental imo, for there not to have actually been a person who started it.