Whether eight or eight hundred survived the flood is irrelevant.
The flood and what happens after it is a new creation. God begins to reestablish the original order of creation after man sins and the entire earth turns to evil. That’s the whole point. It is God’s first step in bringing mankind back to the way it was in the garden before sin entered the world. It is mankind’s first hint that God loves us and has not abandoned us, that he will come to be one of us and he will redeem us, eventually.
God begins to put things right…
Adam: cursed is the ground because of you; (Genesis 3:17)
Noah: I will never again curse the ground because of man, (Genesis 8:21)
It is a new covenant with man…
Then God said to Noah and to his sons with him, "Behold, I establish my covenant with you and your descendants after you, (Geneis 9:8-9)
The covenant is with all Noah’s sons who populate the whole earth. The covenant is therefor with the whole earth - “every living creature of all flesh” - not just the Jews. It is a new creation. God says the exact same words as when he first created man…
*Be fruitful and multiply, and fill the earth and subdue it; and have dominion over the fish of the sea and over the birds of the air and over every living thing that moves upon the earth." (Genesis 1:28)
And God blessed Noah and his sons, and said to them, "Be fruitful and multiply, and fill the earth. The fear of you and the dread of you shall be upon every beast of the earth, and upon every bird of the air, upon everything that creeps on the ground and all the fish of the sea; into your hand they are delivered. (Genesis 9:1-2)*
You can debate the flood itself and number of survivors but whether the flood was local or global completely misses the point. Whether eight or eight hundred survived misses the point. The point is that it is a new creation, a new covenant, a reversal, and the first sign that God intends to set things right in spite of ourselves, that he has not abandoned us, that he loves us. It’s the first hint that Jesus will come to redeem us.
God told Noah not to consume blood because he was reserving the consumption of blood until Jesus…
*Only you shall not eat flesh with its life, that is, its blood. (Genesis 9:4)
**So Jesus said to them, "Truly, truly, I say to you, unless you eat the flesh of the Son of man and drink his blood, you have no life in you; *(Jesus 6:53)
That is the point.