I'm not rejecting Genesis at all.
I'm questioning whether the conclusion you're drawing necessarily follows from it.
If your argument is that Genesis records a mourning context involving lentils, a death in the family, and practices later reflected in halakah, then I agree those parallels are noteworthy.
But observing similarities is not quite the same as proving that the entire later rabbinic institution was already present in fully developed form.
Where I think we may differ is methodological.
You see Genesis 25 as evidence that the later halakhic tradition is preserving an ancient custom.
I see that as a reasonable possibility.
What I hesitate to do is move from "this resembles later shiva customs" to "therefore the later halakhic details are demonstrated by the Genesis account itself."
So I don't dispute the antiquity of the practice.
In fact, I think you've made a good case that some elements may go back much earlier than many people assume.
I simply remain cautious about claiming more than the text explicitly establishes.
That said, I appreciate the distinction you're making.
You're not arguing that rabbinic Judaism invented these customs, but that it preserved and formalized customs that were already present in the patriarchal period.
That's a much stronger argument than claiming the practices originated in the rabbinic era, and on that point I think we are much closer than it first appeared.
