I agree that it's not necessarily a step backwards in the sense of quality of writing or plot, but I do think the subject matter makes a difference. The detective stories, espionage tales, or even the Harlequin Romance novels were different in that although certainly pulpy and low-brow, the characters were _adults_ facing (moreless) adult situations...not wizards, demons, and dragons.
How is that different? There is a lot of "serious / adult" literature that includes wizards, demons, and dragons, and that is not a recent development. (Or in older times, ghosts, spirits, and monsters in general).
Why does it really matter if the setting is more-or-less consistent with now or with recent history, vs older history or extrapolated near-future, or speculative advanced technology (sci-fi), or magic aka "sufficiently advanced technology" (fantasy)?
I'd think the part of "subject matter" that would matter, would be what the problems are. Are the characters trying to stay alive, trying to keep their jobs or get promoted, trying to find the best parties to go to, trying to sneak around while avoiding their parent, etc.
