that there are many many authors of the so called Paul's Epistles. The existence of Paul himself has long been questioned.
Interesting but doubtful, cults usually are started by a cult leader or a tight nit community of collaborators
It’s never some spontaneous grassroots movement that becomes a cult, Buddha existed, Mohammed existed, Shoko Asahara existed, Hong Xiuquan existed, Joseph Smith
So I find it hard to believe that Paul/Saul didn’t exist, there are records of him he didn’t write (when he went to Greece to preach, the Greeks mentioned a weird man came, they didn’t really understand what he was saying, and that "I think he must be advocating for the worship of foreign gods"), and Paul clearly has that central role in Christianity (Jesus had 12 followers according to Christian cannon, meanwhile Paul wrote the fucking bible itself + created Christianity with thousands of followers)
So basing my opinion on this off historical examples (=how these things usually go) and statistical inference I would say it would be at least very unusual if Saint Paul was a made up figure, so I believe he did exist
He was a high ranking rabbi skilled in the arts of psychological manipulation, who either came to believe in Jesus’s cause if Jesus did exist (as he claimed, his story is that he fought against Christians then saw the light and converted), either that or he saw it as a good opportunity to create a vassal religion to Judaism for the gentiles, since Judaism is a racial religion, you can’t convert, but if you create a different sect of Judaism aimed at non Jews, then you can get them in on your system
Also many Jews believe they are the absolute moral authority by default and that all non Jews are evil and immoral by virtue of not being Jewish, if Saul had these beliefs too it could explain why he was trying to make gentiles more jewish, following this logic, a gentile who follows the Torah would be more moral.