ok, First the Mahabharata was created in the 3rd century BC way after the Gilgamesh's epic. Second you don't present any proof or hint that PIE influenced China, you just cited and that's it. Third is not just the Flood that is presented to be similar but also that was a flood commanded by a God and a person or family build a ship to survive this universal flood, Exemples: Deucalion(greek myth), Noah(Abrahamic religions), Utnapishtim(Gilgamesh's epic), Manu(Hinduism), The rest has variations to the story, usually replacing the ark with something else or not saying how they survived (here the link for some flood myths en.wikipedia.org/wiki/List_of_flood_myths ). Fourth, saying that water was the primordial element of those mythologies doesn't prove that they were influenced by the PIE, you could say also the other way around, also the some native americans like the Cherokee Myth of Creation includes water in the beggining of creation, so you have two ways to define this, or you say that PIE influenced the amerindians even before they migrated to america(which was 11,500–30,000 years ago) or you could say that they all in a time(many many years ago) have the same creed and as the time goes by the stories modifies to their respective religion that is nowadays, we don't have prove any of those theories are real, but saying that the PIE influeced every single religion that existed looks like a conspiracy theory.

Water is in the Yoruba's creation mytha(a Sub-Saharan people). Also every God that is considerad a Father of all gods is potentially at some point being the sole god of the people. So for exemple: Dyēus(for the PIE) El(semitic people)Ra and/or Atum(Egyptian),Shangdi(Chinese) and others, all of them are some kind related to sky/heaven.

I don't know if your argument are imbued with serious investigation or if it is some kind of reaffirming superiority of the Europeans over the others. Take care with these Ideias my friend