This is why it is hard for me to follow you lead when you say that
There is a perfect human nature without any predisposition or tendency to sin either hereditary or culturally learned.
It seems like you are treating "human nature" as a "thing" that can be "perfected." But this doesn't make sense to me because "human nature" is a collective abstraction. Of course, we have verses like Hebrews 12:23 that speaks of "the spirits of just men made perfect." But that's different because "the spirits of just men" are not abstractions but realities
. The just men really exist and can be perfected in relation to God. But "human nature" does not "exist" - it is not a "thing" that can be "perfected." Only things that actually exist can be perfected.