No, The Flood was definitely intended to wipe out Sin. All the crossbreeding did not help, but had the offspring been righteous little lambs then it wouldn't have been a problem.
God destroyed the World because in His Omniscience He knew that if He did not, then all Righteousness would have been submerged in Evil.
The Hindus say, in the Bhagavad Gita, that whenever the World is in danger of being overcome by Evil, the Lord comes to reassert Righteousness. In the case of the Flood, Almighty God discerned that no effort to bring the Evil Doers to Righteousness would possibly succeed. Apparently, the Evil ran too deep to instinct -- that these people were no longer 'people', strictly speaking, but malignant animals.
Reading Anne Catherine Emmerich was very instructive in this regards. The Post Flood Evil in the World could hardly touch the Pre-Flood Evil. In the Pre-Flood Days, the Demonic Spirits were both of the Earth and of the Air. The Demons of the Earth had an evil magic that was very substantial. The Flood, for whatever reason, brought a New Dispensation which irradicated the Demons of the Earth, leaving only the Demons of the Air, whose magic was far less substantial.
At the Birth of Christ, even before the Crucifixion, another New Dispensation occured and The Demons of the Air were largely eliminated -- they could not exist in the same Realm as The Christ. Much Diabolical Magic became impossible after the Advent of Christ, because the Demons through which it functioned were displaced.
I suppose the Demons we deal with now, must make sorties out of Hell in order to interact with us -- that they no longer reside side by side with us as they used to.