This is the seminal issue of the Jewish Synagogs and the Christian churches today.
We are at war...if we cannot identify our enemy, we are doomed to failure.
On the other hand...if we can ID our enemy...with God's [G-d's] help...we will be victorious!
were they not drowned in the flood?
Simple minded maybe, but Eph. 6 answered that question for Christians. If Jews don’t want to buy it, then well we told them, so what else is there to do. Let them worry about whether there are Nephilim or what they are. We do know what the devil can do and when the devil is faced square on in the name of Jesus he is forced to yield.