Whatever the reason for the flood, we are left with a very ambiguous relationship with God. From the story of Noah I get a picture of a God seething with anger, and it is only a divine action of creating the rainbow, which self - limits a second or subsequent outburst. Neither humanity or God is any better off. Humanity survived and lives to repeat the former violent behaviour with impunity. The rainbow is there, so a similar judgement, however justified, will not reoccur.
Humanity can do worse things to one another and get away with it.
And of course humanity did, as Jesus was killed on the cross - by those who claimed to be religious. If we use the story of Noah as a basis of our picture of God, then we don't have many alternatives. We can only conclude that God sent Jesus as another, but more persuasive rainbow, not to fix humanity, but as another self restraint on divine anger. The cross is in this view, only secondarily gracious towards humanity. Primarily the Cross shields us from God's anger.