I don't agree that they share the same fantasies, either in their private lives or through their work: Hank Chinaski and Patrick Bateman are so alien to each other in every respect, except for the sense of alienation and disconnection from mainstream society.
Bateman inhabits a very narrow, strictly hierachical privileged society, outwardly at least, he conforms to society and then we see it all disintegrating with the collusion of his peers helping to maintain the facade of normality despite what they see ( as well as being a schizoid,violent, frighteningly empty human being). But I agree both authors tackle the sickness at the heart of society.
I agree about American Psycho being an obsessive wor. and how people will close their eyes to the horror in front of them; by an individual, or society at large, to keep the status quo.