Do christians really think that the elements of the jesus story being virtually identical?

to the much older Mithras, Horace, Dionysius, and others myths was just some really interesting co-incidence. People wrote about Plate, Socrates, and other very large historical figures DURING the time they were living. One interesting thing about mythology is that it was all written AFTER the myths purported lifetime--is that yet another co-incidence. How do you explain these things?