It's actually not irrelevant. The fact that authors would present topics in non-chronological order to emphasize a particular subject or context relates to the "dual" genesis accounts completely. Your minor point about the synoptic gospel accounts not being by the same author is valid, but shows more my lack of time to jump through hoops to present the precise example that would please you rather than any lack of relevence of the original point.
The fact is, some accounts in the gospels in particular are given out of order and often skipping details in between. An example would be when dealing with the miracles that Jesus performed on earth. When reaching that point, the main ordering of the text ends and is supplanted by a "list" so to speak of non-chronological events. This happens because the main timeline story arrived at a point where Jesus' miracles became the focal point and required further clarification. Likewise, the 2nd telling of the Genesis account delves deeper into the special relationship between God and man as opposed to other animals because the subject matter logically needed to follow.
What is irrelevant is your statement as fact that the Genesis myths didn't have only one author. I'm sure the thousands of Doctorate level researchers would be happy to hear that you've finally conclusively proved who penned one of the most controversial accounts of all time. Last I heard, the common consensus was the Moses wrote the Pentatuech....possibly using original source documents or stories passed down from Adam, etc....