Jews had a history of believing that they lost wars when they didn’t listen to their prophets. Jews also had a history of believing that even some of the Gentiles that invaded them were the Messiah. For example, Jewish contemporaries of Alexander the Great thought Alexander was the Jewish Messiah. Source
Roman senator/historian Tacitus says in his Histories 5:13 that:
Few interpreted these omens as fearful; the majority firmly believed that their ancient priestly writings contained the prophecy that this was the very time when the East should grow strong and that men starting from Judea should possess the world. This mysterious prophecy had in reality pointed to Vespasian and Titus, but the common people, as is the way of human ambition, interpreted these great destinies in their own favour, and could not be turned to the truth even by adversity.
So even senator Tacitus thought Jewish prophecies were actually about Vespasian and Titus.
Given that the Ancient Romans invaded at a time when Hellenistic Judaism was popular, I wouldn’t be surprised if Roman invaders also tried to become a Messiah in the eyes of Jews much like how Greeks achieved it. Combining this goal with the goal of creating an explanation for Jewish defeat without losing Roman legitimacy, by inventing a Messiah Jesus that first preached peace & non-violence but later had a second coming in the form of Titus Flavius that used extreme violence as punishment for not listening to the first coming of the Messiah, does not seem that far fetched.
Romans already had a history of engineering and modifying religions in the lands they invaded, so it is not entirely beyond them to do this.
As for Pauline epistles, Galatian 3:16 shows Paul who is supposedly a student of Gamaliel, and a Pharisee of Pharisees does not know enough Hebrew grammar to know Hebrew has no singular for seeds, much like how English has no plural for sheep. This embarrassing mistake by Paul could have happened if Paul used poorly translated Greek source texts of the Old Testament, and his ignorance of Hebrew points to the idea that he was probably at best a Hellenistic Jew. This and his claims that the Justification by Faith has replaced Sinai-tic revelation and attempts to deeply modify Jewish beliefs, and supposed disagreements with the Messianic Jews points to the idea that at the very least he wanted to change Judaism, to become more accepting of the all-powerful polytheistic Roman culture that is taking over. At worst, Pauline attempts to change the Messianic Jews seems exactly the kind of thing Atwill predicted happened when the Gospels were written.
The Messianic Jewish rebels were a major menace before and AFTER the Second Temple was destroyed. In the Kitos war that happened after the destruction of the Second Temple, these Jewish rebels killed 460,000+ Roman citizens. Some of the areas with the heaviest massacres were left so utterly annihilated that others were made to settle these areas to prevent their complete depopulation. See Kitos War.
Only very few people have successfully managed to fight back Rome and live to tell the tale. See what happened to the Druids who resisted Rome, they were so thoroughly destroyed we are not even sure of what they believed. Jews outlived the Roman attempts to erase them. I can see how menacing the Judean rebellion might have been to Rome, given that Judaism survived that time. They will have tried every trick in the book to quench the non-stop rebellion, even to the extent of modifying their religion by inventing Christianity.
While Atwill may have been wrong about some of the parallelomania he exhibits, I think there is a certainly a case to be made for the claim that Romans invented Jesus the Messiah, and later claimed Jesus was a second God to the Jews who only believed in one God.