The logical fallacy that is being used in the passage is B) overgeneralization.
Although there are some narratives written after 1920 that are characterized by their complexity such as William Faulkner's works, not all literature written after that time is difficult to understand. Furthermore, complexity is not a synonym of a lack of elegance or refinement.
There are flaws in reasoning in this passage due to hasty generalization. Overgeneralization occurs when someone unable to consider the whole panorama generalises from inadequate or insufficient evidence and reaches a rushed conclusion about a certain subject. It is overgeneralization what has lead this passage to become an illogical statement.