Good dialogue however I think your definition of the son is incorrect. Adam was once a son of God. The sinful son coming back and being restored is the one that departed the Garden in rebellion.
One can also interpret this parable with the audience involved. The son that stayed was the self righteous Pharisees and the rebellious son were the prostitutes, publicans and other sinners.
I could not argue against your interpretation in favor of mine. They are both spiritual interpretations and correct.