I don't think they really care that the epoch of Gilgamesh mirrors Noah's Ark in any way. In fact, they'd take it as evidence that it actually did happen and that the Bible is not wrong. Almost every religion and myth that came before and after Christianity shares this belief.
I'm no Catholic, and I'm well aware that every religion copied and stole some legends and symbols from their predecessors; they even consolidated holidays because it was politically convenient, not because of any religious significance.
The fact the every religion before Catholicism has this myth makes me want to believe that it happened. Maybe it wasn't global, there's not enough water in the ice caps to cover all landmasses, but if a meteor struck the Northern Hemisphere during the last ice age, tge impact would have caused significant melting. There is evidence that this happened during the Younger Dryas. Every region experiencing this flood would certainly record it in their myths.