If the son of man and "coming down out of heaven" sayings in John 6 are taken literally, it would mean the Son underwent a “de-incarnation"! That is, the Son preexisted as a human person (son of man) and then had to cease being in the flesh ("de-incarnate") in order to take on (resume?) flesh (humanity) again at the virgin birth!
The biblical, therefore better way to understand the teaching is as a reference to the Son of Man prophecy in Daniel 7.
Jesus is that glorified human figure that was seen in a prophetic vision. And the “come down from heaven” is a well-known Hebrew idiom referring to God’s gift to humanity, cp. James 1.17.
