A "very large local one" makes the Ark superfluous. Why didn't Noah and family simply walk away? He had something like a hundred years to do so.
Now you are making the story silly. A flood that would have killed a handful of people does not accomplish the goal. Your version does not even begin to threaten man.
I've long seen the Flood story in Genesis chapter 6 as a parable. A parable is told of course in order to convey some crucial message about life and our choices and relationship with God. And...if a person simply reads, with a listening attitude, the story, starting at verse 5, they will get some pretty profound messages about humans and life. Between just verse 5 and 11, already....
When Jesus told parables, He was telling you and me, anyone willing to be humble enough to listen TRUTHS that are more absolutely true than so called 'facts' that you or I think we know about (!). More True. His Words are more true than your thoughts and my thoughts. So, when we read, we should really listen, and not think we already know. That's another way of saying what I said above.
There is a process that God takes us through (if we are willing) called the renewing of the mind. That means that entrenched prejudices and arguments against the truth of God's word are replaced with the truth. I've had to change a lot of my thinking over the decades. If you read what Jesus had to say about parables, it was to keep the hostile and unbelieving in ignorance and to enlighten those who love the truth. I can see no reason to believe that the Flood account is a parable. The opposite. It sure is a warning that God will eventually call time on the world's wickedness and judgement will be released. Famine, earthquakes, wars, great fear and much destruction will not be parables. Matthew 24: 6 & 7 Neither was God's judgement on Noah's generation. 1 Peter 3:20, Matthew 24:37 & 38 and even the OT, Isaiah 54:9. God said that He covered the earth with water. If God says so, who am I to disagree?
Factual stories in the scripture are often parables also, both at once. Sorry if I caused confusion on that part. It is crucially important not to get stuck arguing mere physical particulars and miss the key messages. If someone emphasizes stuff physically about the flood, they might be to caught up in useless arguing and missing the meanings, the life changing messages.
It seems the Ark would have been a death trap with only a single window 1 cubit square. The seaworthiness of the Ark would have been irrelevant, because everybody would have passed-out and died from the bad air before the flooding had even started.
So if Christians draw the same lessons from the story whether it's taken as literal history or not, why is it so important that it be literal history? It's still the inspired and authoritative word of God either way.
In a way, you are right. The problem is, where do you draw the line? Was King David a real person, or a myth? I believe him to be real. If he is real, why not Noah? Was Moses real? Lord Jesus spoke of him as if he was - as He did with Noah. How about Abraham, Isaac and Jacob? God calls Himself the God of all three men. Is He the God of myths? Paul stated, 2 Timothy 3:16 "All Scripture is God-breathed and is useful for instruction, for conviction, for correction, and for training in righteousness...."
It's not really an issue about whether any of those individuals were real. Ultimately it's an argument about the text itself. Are those stories accounts of those (very likely) real people written according to the historiographic standards of the day? Or are they literal and inerrant--meaning that you can decode things from them that may not be directly related to the narrative? As, for example, YECs decode the age of the Earth, which nowhere stated or considered in the Bible.
