What the stone may indicate is that like other religious story tellers, Christians claimed earlier stories as their own. The book of Esther is often cited as an example of the Jews appropriating Babylonian mythology as their own.
For instance, Buddhist stories have walking on the water and a wedding miracle as part of their tradition centuries before Jesus was supposedly born.
The slaughter of the innocents under Herod is mentioned nowhere in any official record of the time and no contemporaneous source. Josephus, a Jew, who chronicled the Jewish revolt that led to the destruction of the second temple doesn't mention it.
It is obviously a retelling of the story of Pharaoh ordering the killing of the newborn of the Hebrews to get to Moses. Jesus even flees to Egypt.
To an objective observer,this would mean that Jesus' birth story borrowed from early Jewish stories and his resurrection story was a retelling of the Simon story on the stone. Borrowing is just another form of embellishment
Embellishment happened with Buddha and Muhammad too. In the Early Buddhist tradition, Gautama was born in the traditional way. Later he was born from the side of a white elephant and it rained flowers. During Muhammad's life he was a prophet. Later tradition added:
"In Islam, the Prophet Muhammad's night journey from Mecca to Jerusalem prior to his famous trip to heaven is called Isra'. As alluded to in the Qur'an (17:1), a journey was made by a servant of God, in a single night, from the “sacred place of worship” (al-masjid al-haram) to the “further place of worship” (al-masjid al-aqsa).
Traditionally, there was general agreement that the servant of God was Muhammad and that the “sacred place of worship” was Mecca. Early commentators, however, interpreted the “further place of worship” as heaven, and the entire verse was considered a reference to the Prophet's ascension into heaven (Mi'raj), an ascension which also originated in Mecca. In the period of the Umayyad caliphate (661–750), the “further place of worship” was read as Jerusalem. The two versions were eventually reconciled by regarding the Isra' simply as the night journey and relocating the point of Muhammad's ascension from Mecca to Jerusalem to avoid confusion. Some commentators also suggested that the Isra' was a vision sent to Muhammad in his sleep and not an actual journey at all; but orthodox sentiment has emphatically preserved the physical, thus miraculous, nature of the trip.
The Isra' story, greatly elaborated by tradition, relates that Muhammad made the journey astride Buraq (q.v.), a mythical winged creature, in the company of the archangel Gabriel. Muhammad meets Abraham, Moses, and Jesus in Jerusalem; he then officiates as leader (imam) of the ritual prayer (salat) for all the prophets assembled and establishes his primacy among God's messengers."
http://www.geocities.com/khola_mon/myth/Miraj.html
The reasoning is lacking. Just because some stories from some religions seem to have borrowed from earlier stories means nothing, especially in this case. If the people who made these tablets used the old testament to predict what they meant and they accurately understood the prophecies to be predicting the death a resurrection of the Messiah after three days, that in no way conflicts or suggests they were borrowing. It means the Old Testament prophecies were accurate. Jesus was not meant to be a new religion, he was meant to be a fulfillment of the old one. The fact that older writings foreshadowed Christ serves as verification, not as proof His story was copied.