The sixth argument I would offer is that there is no clear motivation here for a Christian scribe to invent and insert into to Josephus a text like this. What would he have hoped to have gained? Who was he trying to fool?
The notion that this was done somehow to plant evidence that Jesus existed is
entirely anachronistic. No pagan or Jewish critic of Christianity at this time doubted the existence of Jesus, and no Church Father ever had to defend that idea.
The theological controversies of the day centered on Jesus' divinity. And yet the author of the TF, at best, simply tells us that Jesus is the Messiah. This seems like a pretty low Christology for a Christian of the late-3rd or early-4th Century, when this interpolation is thought to have occurred.
Even if we assume some motivation for inventing the TF out of whole clothe, what would be the purpose? It's not like there is only one copy of Josephus' work at this time. As Eusebius points out, Josephus' works were deposited at the Roman public library. And so anyone could have compared the first interpolated copy with any other to show it was a forgery.
Eusebius, History 3.9, wrote:
[Josephus] was the most noted of all the Jews of that day, not only among his own people, but also among the Romans, so that he was honored by the erection of a statue in Rome, and his works were deemed worthy of a place in the library.