Actually wiseman proposed that the hebrew toledoth actually didn't mean genealogies. A better translation would be 'histories.'
Wisemen i think was the first to suggest that the toledoth statements in Genesis were colophon statements rather than titles, that is they were summary statements placed at the end of the sections rather than the beginnings.
And you are right, the tablet theory completely destroys the charge of 2 creation accounts. There's actually only one creation account. What follows is an account about Adam's history in the Garden of Eden, the Fall, and the Cain and Abel affair.
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