Genesis 6-9 vs. the Gilgamesh Epic

The account of the flood is very similar in both of these accounts. I have often heard stories from non-Christians that the biblical accounts borrowed from other sources. I assume that this is an example of one of them. What I cannot understand, though, is why the Bible had to borrow from Gilgamesh and not the other way around. Although both accounts have supernatural elements, the Gilgamesh Epic seems far more legendary and legendary accounts are typically the ones that are said to have borrowed when another similar account exists that is not so legendary/mythological. Gilgamesh is on a quest to find immortality. On his quest he meets Utnaphistim who found immortality through surviving a flood that has some characteristics common with the flood Noah survived. This is a hero story, not a historical account. Noah, however, is presented not primarily heroically, but as a normal man (and a naked drunk on at least one occasion) called for a special time. In man’s sin nature he is quick to prefer anything to the Bible, but just because something seems to be similar to the Bible does not mean it came before the Bible. The existence of similar stories should actually act to strengthen, not diminish, the biblical account. Multiple sources point to the event as actually having happened.