The Council of Nicaea was super important historically, but not in the way people think. It did not anathematize beliefs like reincarnation; they did not decide to keep the Gnostic Gospels and other "heretical" works out of the Bible, etc. and etc. By the time of the C of N, proto-Catholic/Catholic Christianity was already well established. Beliefs like reincarnation were no longer on the table if they ever were. The New Testament was pretty much what we have today. Nicaea was mostly concerned with the nature of Christ and the Trinity.
That being said, early Orthodox/Catholic Christianity was definitely a psyop in effect, and a lot of this can be seen in doctrines and beliefs like the Trinity. Threefold Godheads were nothing new. They were sort of a trope in ancestral Indo-European religions. But now you had to believe a very specific thing about how the members of the Trinity were related to each other, a thing which made no rational or irrational sense. If you tried to "help" by sorting it out in such a way that it made sense, you were very likely to be branded as a heretic and to have that heresy named after you. The result: masses of people believing something that was flagrantly nonsensical, and deathly afraid of trying to think about it for fear of punishment in this world and the next.