The Christ myth theory isn’t tied to Frazer. That’s the genetic fallacy and a red herring.
Osiris dies and is physically resurrected, as I explain in the article linked below. See also Richard Carrier’s article on the dying and rising gods (second link). You're confusing identity and similarity, though, when you say a resurrection story has to be just like Christianity's version to count. It's an ideal type, and the concept is of a divine being that somehow falls (suffers badly or dies) only to triumph in the end. Christianity fits that type, as do lots of other ancient religions. The rest is details.
Also, see Jan Assmann on how Egyptian religion originated the ideas of personal resurrection and divine judgment way before Christianity. Paul doesn’t remotely originate any of that. Indeed, the personalization of immortality, or the transition of the seasonal notion of resurrection into a personal, moralistic one happened in the Greco-Roman Mystery Religions, too, as part of the Axial Age’s revolution in spirituality. Zoroastrianism is another source, which impacted Christianity via Judaism during the end of the Babylonian captivity. Christianity is a latecomer to all of that.
Your explanation of the origin of the Christian resurrection idea is a move in rationalist theology that takes the New Testament too seriously and literally, in my view. Rationalist theology naturalizes all the miracles. So, we assume the miracle story is somehow literally correct, but the narrative is alleged to have arisen from a misunderstanding of a natural event. For instance, Jesus’s tomb was robbed, and later Christians garbled the truth with the resurrection narrative.
I mean, it’s possible and way more likely than a divine resurrection. But why would Jesus have had a private tomb at all? Why wouldn’t his body have been thrown into a lime pit that acted as a mass grave? None of the empty tomb story should be taken literally. It’s a literary device to compensate for the horror of what would have happened to Jesus. The gospels were written by apologists rather than eyewitnesses, decades after the fact to instruct Christian communities that were living after the destruction of Jerusalem.
I’m interested in Gnosticism too. In my writings I combine some of that with cosmicist pantheism and existentialism.
