Well… It’s not so much that the stories are simply exaggerated as the authors had different ways of conveying a story than we use. We want to dismantle these stories on scientific levels, but the author is completely unconcerned with painting a naturalistic picture he wants us to see God’s work in creation. Let’s look at the flood story in Genesis 6-9 as an example:
6:12 And God saw that the earth was corrupt; for all flesh had corrupted its ways upon the earth
In our scientific mindset we often look at the “all” and think it means every single person- no exceptions- but if we look at verse 9 above we see Noah is an exception. Theoretically there could have been other exceptions as well. Obviously this all is meant to convey a general state of humanity rather than a literal statement that each and every person is corrupt.
6:9b Noah was a righteous man, blameless in his generation; Noah walked with God.
Was Noah the only righteous person? This verse singles out Noah as righteous, it makes no judgments on any other person. Yes, we know from verse 12 that the tenor of society was evil, but this verse does not mean Noah is literally the only righteous person on earth. Rather Noah is the example the author gives us. In other words, the Bible is not trying to tell us in a scientific sense. Noah was not necessarily the only righteous person, he is simply the only righteous person the story cares about. The story does not say Noah is the only person to survive, but that God protected the righteous; we cannot look to the verse for scientific evidence that all humanity is descended from Noah. This becomes a theme for later texts.
7:12 The rain fell on the earth forty days and forty nights.
We hear the days and think it rained for a month and a half straight, but the author is setting up a theological scene. The number 40 seems to represent a long time perhaps because of the relationship to generations being marked at forty years. Anyway the author wants us to recognize that it rained for a while, it took a long time to undo the creation God had made.
7:19 The waters swelled so mightily on the earth that all the high mountains under the whole heaven were covered;
Again, we hear the word “all” and think scientifically of the entire globe being covered. Yet the author had no concept of the globe, he was making a theological statement. In Genesis 1 God brought dry land out of waters of chaos by a divine command. Now God is rescinding that command and the waters of chaos can return. The message is God does not tolerate evil and will withdraw from evil and when God does this, chaos comes takes charge. The author is not making a case for a “global” flood as much as the author is showing what happens when God withdraws.
7:21 And all flesh died that moved on the earth, birds, domestic animals, wild animals, all swarming creatures that swarm on the earth, and all human beings;
Again, notice the word “all” it is used to mean that God destroyed the old system, with the purpose of destroying evil. Yet, God left Noah alive and the old evil buried in humanity will resurface again for God to deal with again. How do we know this is not a scientific statement: Numbers 13:33 “There we saw the Nephilim (the Anakites come from the Nephilim); and to ourselves we seemed like grasshoppers, and so we seemed to them.” This passage in Numbers says the Anakites are descended from the Nephilim whose appearance in Genesis 6:4 is part of the runup to the flood story. In other words, some of the Nephilim physically survived the flood to produce children. Does this undermine the flood story? Obviously not because Jews would not have included both texts among their sacred Scriptures if one of them completely undermined the other one. And yes they would have caught that, early Jews memorized all of Genesis, Exodus, Leviticus, Numbers, & Deuteronomy.
All of this works together to tell us the author of Genesis had radically different expectations from the story than those of most modern Bible readers. I would also point out that the flood narrative is pretty universal among ancient cultures and so almost certainly has a basis in a real (and extremely large) flood. Yet, while each of the ancient authors has this story the Bible is unique (as far as I know) in its rationale for why the flood happened. The Bible is the only version where the flood comes because humanity is evil, and the deity demands righteousness. We must take that uniqueness seriously. One other issue is that one should not allow this reading to omit the miraculous in the stories. We cannot simply say the author is telling a story and skit past miracles as simply artistic embellishments. Notice the basic miracle, God saving Noah’s family from flood, is probably true; it is the storytelling around the miracle that pushes us to ask questions.
If you want to dig deeper
Also read John Walton & Tremper Longman III The Lost World of the Flood: Mythology, Theology, and the Deluge Debate& John Walton The Lost World of Genesis One