I haven't heard that about the Egyptian myths - usually it's a claim that Christianity arose on the back of the Dionysus myth.
But even if there are parallels... and there are, I think it should bolster the faith instead of challenge it.
For C.S. Lewis these links to myth were a major factor in his conversion to Christianity.
Here's an interesting quote:
According to Humphrey Carpenter, C.S. Lewis’ conversion to Christianity was directly linked to his passion and understanding of paganism. In Carpenter’s article, which appeared in “The Inklings” in 1978, he describes several significant conversations Lewis had with his colleagues at Oxford leading up to his conversion. According to Humphrey, Lewis had come to believe in the importance of myth, but was not yet convinced that myths were anything beyond “lies,” beautiful and inspiring as they were to him. The concept of myth and its role was the topic of conversation between Lewis, JRR Tolkien, and Hugo Dyson one night in September of 1931. On one of their many walks around Magdalen College, JRR Tolkien explained to Lewis that myths were not merely lies because humans are not “ultimately” liars. The very human act of making myths, “mythopeia,” to express truth, was also part of God’s self-expression of eternal truth. Tolkien went on to say that just as God had expressed his truth in the images and poetry of pagan myths, so God had done so in Christianity; the difference being that in Christianity God used “real people and actual history.” At that point in the conversation something suddenly clicked for Lewis and he was able to equate the old “dying god” myth of paganism with the dying Christ that led toward a full embrace of and belief in Christianity. From that point on, Lewis viewed Christianity as the “myth become fact.” This concept was central to Lewis’ conversion. Lewis would later write in his autobiography of his conversion experience, “Sometimes I can almost think that I was sent back to the false gods there to acquire some capacity for worship against the day when the true God should recall me to Himself.”