Christianity doesn't really stand by itself, by which I mean you can argue there is hardly any unique elements/symbols in it, when coming at it from a comparative mythology standpoint. Perhaps the BIG unique element is the emphasis of the historicity of Jesus. But, if you look back at the Ten Commandments which really is the first major "instilling" of moral development in the whole Judaism/Christian storyline, they had a parallel development over in Babylon where Hammurabi received tablets containing laws from the God Shamash, which arguably predates the Moses story. There are other parallel collection of laws beyond these two, some of which predate Moses story and some that come after. So, all these developments are intertwined. (Campbell even shows how some of the developments taking place going from the Old Testament to the New Testament were also paralleled in the East going from Hinduism to Buddhism, but over there it happened 500 years earlier!)
I think what you have in the West is a strong development of the ego and sense of individuality that has taken place as the "western" patriarchal religions have developed over time, culminating in the Christianity and Islam that we have in the world today. Erich Von Neumann goes into this in depth from a psychological standpoint in his Origins and History of Consciousness. I've long argued this is the explanation for where materialism comes from, as well, which also means materialism has been in the making for 1000s of years and goes well beyond just the usual modern technological interpretation of it, which is a small part of it. (It also means modern-day exoteric western religion is as much a "victim" of materialism as science is!) You could also argue this is where any modern-day nihilism ultimately came from, as the seeds may have been planted a long, long time ago. It's only via a greater sense of ego/individuality, as talked about by Neumann, that enables one to feel separate from and thereby shrug off the "Cosmic Order" mentioned in Nietzsche's ideas above.
Egyptian myths are neat because they contain greater amounts of elements from both the earlier matriarchal myths and the newer patriarchal myths. I still remember reading a book on Osiris by E.A. Wallis Budge. I had to check the cover every now and then to make sure I picked up the right book, because I kept thinking I was reading about Christianity! The point Budge makes is how much the story of Jesus was already pre-figured in the Osiris/Horus myths. This happens enough that some philosophers have said things like Schelling says here:
"In the pagan religions, Christ was implicit; in the Old Testament prophesied; and in the New Testament revealed. Thus, Christianity is innate and as old as the world"
[Paraphrased and totally butchered, I'm sure, but it gets the point across]
So, I guess that is a (very?) long-winded way of saying I have a hard time looking at Christianity in isolation on issues like this. To me, it's like trying to talk about the evolution of a certain species, while ignoring what came before it and the environment it interacted with while developing.