It's a bit farfetched to require a written document to be memorized, turned into an oral tradition, and then written down centuries later in a different language by Moses. It's much easier to have the written documents (clay tablets) carried from Sumer to Egypt where they could be "read" (translated) by Moses (and his associates) several hundred years later.
In fact, the Hebrew tradition post-Moses is that they carried about the tablets Moses received from God in the Ark of the Covenant.
Fair enough. So since Gilgamesh far predates any extant fragment of the Bible, we should consider it the more reliable text, no?
(It's a better story, anyway)
Why? The stories that were written down were based on oral traditions, which continued to exist as oral traditions among the common people, who were generally illiterate. Abraham probably received the oral tradition from his parents, took it with him to Caanan, and passed it down to his descendents, who eventually wrote it down after the Kindgdom was established.
If Abraham brought the writings with him from Messepotamia, then there should be some archeological evidence of Summerian writing in Caanan from the time before the Israelites went to Egypt. In fact, we don't.