Hi Lumen
Not entirely sure I understand your concept that..." The absence of these two characters does nothing to eliminate the concept of Original Sin."... 
If the concept of original sin is based on the idea that there WAS a sin, then there is no longer a basis for it. If there was no one to commit the sin, the concept of an inherited sin has foundation.

If you mean that myth stories are based on common human lived experience, I would agree with you. we evolve from organisms that die, and death and struggle are part of human existence. We easily mis-use our free will to choose things contrary to our own good and the good of humanity and creation. We 'sin' as easily as the myth pictures 'Adam and Eve' as sinning.

Perhaps it depends on what your 'faith picture' of 'Original Sin' entails. 

I would suggest that much of what we traditionally have ascribed to an 'inherited guilt' and 'fallen' nature and much else, is no longer Scripturally and Theologically tenable.