I just think it's not ultimately important whether the movie we see is the one he's writing. It's a story about a man grappling with his moral code vs the constraints and expectations of the genre he's writing in. I think people's familiarity with Adaptation is messing with people's expectations, because they recognize a sorta similar setup and then instantly expect the rest of the movie to neatly do the same thing in terms of Meta structure. I personally don't think every screenwriter meta-commentary story has to neatly wraparound like that, and I don't think they were really going for that in this movie. Its inherently a more playful and less realistic comedy that's messy and plays around with structure. I'd say if anything it's closer to the Big Lebowski or Kiss Kiss Bang Bang.