Interesting, but the commentary in the first 3 bullet points admits to not knowing how the stories are linked, but assumes they were copied somehow anyway.
Let me put a different spin on this to see how open you are to being possibly wrong, your response will be very telling:
I told 100 people about how I escaped a hungry pack of lions while hunting one day in Africa. I escaped by killing one of them with a shot gun blast, stabbed one in the eye as it was chasing me up a tree, killing it, and then the others decided to leave. These 100 people then moved to different parts of the US, and told this to their friends.
Upon returning to the US myself, I'm hearing stories ranging from me fighting lions with my bare hands, to dropping a grenade down a lions den to escape -- none of which are true. When people retell this, by the time it gets back to me, it's completely different than the original.
Does this mean a flood of any proportion happened? No. Does this mean any myth has even a little veracity? No.
All this means is that the similarities can, and are likely, a product of people retelling the same thing, but adding or exaggerating details.
Open your mind to other possibilities, then you'd have a more coherent and complete conclusion without a big of gap that I just exploited.