***The discarding of the bulk of humanity, in apparent opposition to the bulk of the Bible does not make sense to me.***
Maybe you are looking at the wrong bulk? Most of the OT is about one tribe killing another, one people wiping out another, nations destroying nations, people subjected to slavery, and the whole world except for eight destroyed at one time.
I see a huge difference in the tribal warfare and physical killing of the OT and in the Protestant belief of creating the bulk of humanity in order to condemn them to hell.