The essence of gnosticism as I’ve always understood it, Kolo, is not that they posited man as a spiritual being, but that they insisted that God would not become an earthly being. Thus, John’s words about God becoming flesh and dwelling among us. Also, John’s words about those denying that Jesus (the Christ) has come in the flesh.
Therefore, to suggest that the original human lived in a spiritual realm that we no longer inhabit is to ignore the angel with the flaming sword guarding Eden.
To suggest that a human is both spirit and body is to ignore the entire testimony of the bible, but especially of Romans 7. Such a belief is not gnostic; it is thoroughly Christian.