Wait...
Gil = 2/3 Divine
Therefore:
Father = 1/2 Divine
Mother = 1/1 Divine
Therefore:
Grandparent 1 = 0/1 Divine
Grandparent 2 = 1/1 Divine
...
If:
Grandfather = 0/1 Divine
Then:
Grandfather banged a goddess and Father banged a goddess.
But:
Gil rejected a goddess.
...
Conclusion:
Gil's line was one step away from true divinity, but Gil rejected that last step.
Ergo:
Gilgamesh is in fact a disappointment to his family's line.
...
Huh...looks like the King of Heroes really fucked up back there.