Your synopsis is the most spot on I have ever seen by any poster, and you get the "Winner" tag from me. Why others haven't realized what you posted baffles me, but when you look at humanity and its progress, it has not stepped out of the primitive days yet. I wrote a short book, not yet published, of how human indoctrination takes place, and it starts with the caveman and progresses to unified tribes and then to Greek gods to explain calamity and hundreds if not thousands of other invented god concepts. Christianity plagiarized and borrowed from those. You are correct that the Roman Empire adopted it and if it weren't for emperor Constantine, a ruthless mass murderer who killed his own wife and son (and the Catholics made him a venerated saint) who saw that Christianity would be an aid to him in controlling the populace to keep it in fear that there was an invisible god enforcer.
The high priests then went into warp speed after languishing for 300 years because many people believed Jesus was "just" a son of God. Inventing the Trinity was a master stroke and Constantine lit the fuse of what would become billions of believers today by showering the priests with new churches, land and money. As it happens religion became government and became ruthless and unfortunate as it is, killing and torturing people for not believing is a very powerful tool to create belief in new babies, passed down through the genes of all those who witnessed the earthly horror of not believing.