Factually, the text of the Qur'an has not been preserved perfectly. The text has additions, deletions, conflicting manuscripts, and variant readings like any other ancient writing. Logically, it is irrelevant whether the text of the Qur'an has been preserved because preservation does not logically imply inspiration. A book can be perfectly copied without implying its inspiration. The character of someone is no indication of whether he is telling you the truth.
Good people can lie and evil people can tell the truth.
This argument is erroneous for several reasons. It is a false analogy to parallel the pagan origins of the rites commanded in the Qur'an with the present day holidays nowhere commanded in the Bible. It is irrelevant that some Christians choose to celebrate the birth of Christ. Since the Bible nowhere commands it, it is a matter of personal freedom. But Muslims are commanded in the Qur'an to believe and practice many things which came from the paganism of that day.