But the gospel writer Mark [who was an associate of Peter (who was actually at the transfiguration)] doesn't use the phrase "Son of God" when describing God talking. He says He calls Jesus his "beloved Son".
Mark 9:7 And there was a cloud that overshadowed them: and a voice came out of the cloud, saying, This is my beloved Son: hear him.
Mark 9:8 And suddenly, when they had looked round about, they saw no man any more, save Jesus only with themselves.
Mark 9:9 And as they came down from the mountain, he charged them that they should tell no man what things they had seen, till the Son of man were risen from the dead.
If skeptics and Ehrman want to believe the above three verses from the Gospel of Mark just refers to a prophet who predicted himself rising from the dead -- that's your right.
ETA: I know of no prophet in the bible who was called "My beloved Son" by God and I know of no prophet that predicted he would rise from the dead.