I got the right answer through the process of elimination but was very fixated on the word "unambitious" as I feel like that didn't have any support from the passage. I paraphrased the critics' position to be "Don't venture out of detective fiction, remain true to detective fiction," but I don't know whether detective fiction itself is an unambitious literary genre and that seems to be a bit of a stretch that bothered me about this answer.
Could anyone could explain this, thank you!