Yes, someone definitely created the fictional god named jesus. Whether it was Paul or some Roman emperor, I'm not sure. But the entire jesus stories are just that...stories. They have no basis in fact.
http://mama.indstate.edu/users/nizrael/jesusrefutation.html
It does have basis in fact. The problem with the link you shared is that pretty much none of it is true. Or the "facts" leave out important ideas. For instance, in the talk about the mother of Jesus, Mary. It claims that Mary was an adulteress. Yet there is no evidence of that. It then continues with how virgin births were common. Not at all. There are miraculous birth stories, but not virgin birth stories. In that, Jesus is unique (Mithras may have a virgin birth story, but that story did not evolve until after the time of Jesus, when it was a Roman religion, not a Persian one).The idea of these virgin births don't exist until about the last century or so. They don't exist in the actual stories.
The one particular god they single out is Tammuz. Tammuz was a Sumerian god who later was adopted by the Babylonians. Some Hebrews may have entertained the idea of Tammuz, but worship of him had long died out by the time of Jesus. It is true he was called adonis. But the term simply means lord. As in, it translate to lord. It really means nothing. Its like me calling Tammuz a god. Doesn't mean I worship Tammuz, or really think that Tammuz exists. It means that god is a word the described the character.
The problem with Tammuz, or Dumuzi, is that very little is known about his origin. By the time that he was being worshipped in Babylonia, he was already a very old god, and much of the writing about him was gone. To claim that Tammuz was born of a virgin then simply is making things up, or relying on works that can't cite sources, as there are no real sources.
Your source goes on to say that Mary, the mother of Jesus, and Mary Magdalene, were once one and the same, and later split into two individuals to argue that mother Mary wasn't an adulteress. This makes no sense. It argues against the virgin birth story then, as that supposedly was to solve the problem. That and Mary Magdalene is never said to be an adulteress.
Now, that is only a very small section of the source you provided, and it happened to be the place where I stopped scrolling, but in just that small area, we can see that the source is making things up, or is seriously out of touch with actual scholarship on the subject. There is no reason to assume that rest of the source is any better.
Jesus existed. That is a historical fact. What his exact nature was can be debated, but that a historical figure did in fact exist is a certainty.
Pre-Christian Roman religion was important (success) in the Empire. The importance of unity of belief of all citizens is evidenced by the Roman efforts to force statues of Roman gods into Jewish temples. The word "catholic" means "universal". "Roman" "Catholic" - "Universal" religion of the "Roman" Empire. Rome had conquered many diverse peoples and the new religion incorporates elements of so many beliefs/cultures: Greek, Roman pagan, and Jewish. Unity in the Scriptures: "All things to all people", at Pentecost they all understood even though different languages, "That they may be one", "There is no longer Greek or Jew".
There were sporadic attempts to put Roman statues (usually that represented the current Emperor, a deity himself) into the Jewish Temple. It had nothing to do with unifying the empire though. It had to do with making the Jews know who really was in control. And each time, it was met with great revolt, and often, it was an action Rome backed down from.
We can actually see that Rome didn't care if the religions were unified, as Jews were given special privileges under Roman Law, which dealt with their religious beliefs. It is also the same reason why there were competing religious thoughts in the Roman empire.
The word Catholic does mean universal, but has little to do with the Roman Empire. The term, when applied to the Christian church, wasn't used until the second century, a time in which the church was still being sporadically persecuted by the Roman empire. It was picked up by Christians as way to unify Christian thought. In effect, it set them up directly against Pagans and the Roman Empire (an empire they consistently criticized). By the time that Christianity was adopted, it had taken on a new context, one that meant orthodox. Again, it wasn't to unify, but to separate christians into either orthodox thinking, or heretics.
As for there may no longer be Greek or Jew, it continues with in Christ. That means a whole lot, as Paul isn't talking about everyone, but specifically about those who believe in Christ. It unifies Christians, or those who take on that idea, but it separates all others.
That is why Rome would sporadically persecute Christians, as well as others. It wasn't to unify people.
If the Romans wanted to appeal to the common/peasant Jewish people while also turning them against their Jewish leaders, doesn't much of the Christian Scriptures fit that?
Rome didn't take up accepting Christianity until Christianity was already quickly spreading, and becoming a major force. They took advantage of Christian popularity. Before that, there were attempts to persecute Christians.
By the time that Rome accepted Christianity, Judaism was in pretty harsh terms. Christianity definitely wasn't seen as an appeal to Jewish individuals, but more of an enemy.
"It really didn't unify"? I think it did quite a bit and what was leftover of paganism was dismantled and the Jewish Temple had already been destroyed a century or so earlier. So, it unified in the sense that what was left over was minority groups and Judaism became a minority group in the Roman Empire for centuries following.
The problem is that you aren't looking at history in its actual context. Once the Jewish Temple was destroyed, a rift happened between Jews and what would be Christianity. So no unification there. And at that time, both were minorities. Even by the time that Christianity was allowed, such as in the fourth century, Christianity remained a minority. It was just one more religion that was accepted.
Paganism wasn't being dismantled, and still, as a whole, was dominate. It wouldn't be until much later that that would change.
Now, does the fact that the unity aspect played into Roman Empirical motives, mean that Christianity was promoted/fabricated by a powerful empire with its own motives? I don't claim to answer that question except that there seems to at least be Roman influence. Was St. Paul in some cooperation with the Romans? I don't know. It does seem that if one wanted to unify an empire including Jewish people, then one may sponsor a highly educated Jewish man (Saul) who also knew Greek, to help formulate theology for all in the empire. Perhaps the initial 12 disciples were not as educated and so were not as able to do the job
Here's the problem. The fact that you're talking about, Rome finally accepting Christianity, at least to a point, to try to help unify anything, didn't even begin until the fourth century, and only then to a point. By that time, the major ideas of Christianity were already cemented. The canon was fixed, the story of Jesus had long been written. Rome couldn't fabricate anything, because the religion was already created and had been moving forward for hundreds of years.
Was Paul in cooperation with the Romans? No. In fact, he was imprisoned by the Romans. He was persecuted by the Romans. And after him, Christians were persecuted. Rome didn't give a crap about Christians, besides using them as a scapegoat, until hundreds of years later.
There was no unity, and by the time Paul died, the unity between Jews, and what would be Christians, was already extremely tense. In just a few years after Paul's death, the two would really hit a breaking point and split. From there, Christians would have major problems with not only Jews, but also Pagans, and Rome itself. There was no unity.
The problem with your theory is that you aren't looking at history in context, but are taking things that happened four hundred years later, and assuming that it has any relevance to the time of Paul, which it simply doesn't.