I think yer sort of half-right. But you forget about Seth.
A few gnostic traditions follow your same line of thinking, though both Cain and Abel were the same "race". Cain killing Abel was the metaphor for that 'race' turning towards evil.
What about Seth?
Seth was the third son of Adam - as conceived through Eve. The only one that was 'truly human'.
It's important to point out that there is nothing wrong with these other 'races'. They aren't born evil. They aren't predisposed towards evil - any more than the rest of us are. The only difference is the 'owner' of the race. At least as it was at the time. Like each creator build himself a little army and said 'these are my chosen people - those are your chosen people'.
Just thought I might share another perspective.
I think you hit the nail on the head.
The sleep is the forgetting of the truth. The bible says God caused Adam to fall into a slumber. Never does it say he ever woke up.