“The Apostles were witnesses to Mary’s death,”
The Synoptic Gospels were written prior to the fall of Jerusalem without any mention of the death of Mary. John, the Apostle to whom Jesus entrusted Mary wrote his Gospel and letters around 90 A.D. without any mention of Mary’s death. Luke wrote his Gospel and Acts before the fall of Jerusalem. In Acts he mentions the death of the Apostle James but no mention of Mary’s death. Peter does not mention her death in his letters and even her son James failed to mention her death in his epistle.
There is no basis for the statement that the Apostles would have highly cherished Mary’s relics when there is no evidence they treated her death any more highly than any one else in the church community; in point of fact, there is no evidence that the Apostles cherished any relic of Jesus except His memory, words, and deeds.
John said quite plainly in his Gospel that he did not include everything of importance. There is no basis for claiming that the Assumption of Mary did not happen because it was not reported in the Gospels.
You are arguing from ignorance, a big logical fallacy.