The story of Bereishis is the story of the failure of oldest sons. Yishmael and Esav are bad guys. Reuvain sleeps with his step-mother. Efraim is favored over Menasheh. Then in Shemos, the ultimate punishment is the killing of the first-born sons. Who resents first-born sons that much? You'd think all this was written by a second-born son who'd been abandoned by his mother as an infant or something.