The truth is NO ONE denied Jesus lived and was real, except people like you that haven't looked into it. Even atheists didn't deny it. I would like to mention there are things that have been taken from Paganism, and put into Christianity, but it was to convert Pagans. For instance changing the day of worship to Sunday, and like you said the date of Jesus' birth. But none of this doesn't mean Jesus didn't exist. This cannot be denyed by anyone who has looked into it.
Josephus mentions many facts about Jesus' life.
Thallus mentions the Darkness During The Crucifixion.
Celsus stated many facts about Jesus.
Julian the Apostate (A Roman Emperor from 361-363 A.D.) who was an enemy of Christianity wrote about the miracles of Jesus.
Jewish Rabbi, Eliezer ben Hycranus of Lydda wrote about the miracles of Jesus.
Atheists inspired by visions and became Christian:
Alexander The Great (Atheist)
Paul (In the Bible) (Atheist)
These are only famous people that have been recorded into history.
Also think about this. What would it take for you to go out and tell people about Jesus, even though you knew you will probably be killed like the disciples did? The ONLY thing I know of would be if I had seen Jesus alive after he died. Do you think the disciples would have done what they did without such proof? Do you think the disciples got together and said lets preach to the people and start a new religion, even though we will die, and fool everybody, and have 11 out of 11 do it? Not possible.
"Virtually every page of the gospels were plagiarized from earlier pagan myths."
The fact that Jesus lived has already been proven. There are also many statements in the Bible that have been proven by Archeology. So your argument has no legs to stand on.