He did have a co-writer, but given how all she wrote for before this was a few TV episodes and short films, Druckmann basically had complete control over this game's direction and the like.
Dang it, this is yet another case I've sadly seen all too often. Due to the success of the previous work, a creator is basically given carte blanche to do whatever the holy heck he or she likes with absolutely zero restrictions, and said creator has lost his or her mind as a result. Given how Heenig and Straley aren't with ND anymore, Druckmann no longer had those people around to tell him "no, that's stupid and we aren't doing that." He effectively had free reign over the company and the game's direction.
You know, for as much crap as executives get from people like Jim Sterling, games like these show why they still are necessary, because giving someone like Druckmann no meddling or vetoes whatsoever has led to this crap. Doesn't help either that journalists are so fricken enamored with the concept of "auteur theory" that they applaud stuff like this, especially if it falls under their agendas.