The crossover writers might be newer, but they're among the most rigid writers we have stylistically. They're also among the weakest, with a few exceptions.
-- I don't see "LJ house style" as particularly good, because of its restrictions. What puzzled me about it is that although it's clean, it's limiting, and I don't see that as one of the progressions from first and second wave to current writing. But again, Highlander seems to have followed a different progression.
For example, while we never indulged in crack!fic, two years ago we did have a brief flowering of experimentations in style. Rather than growing and progressing, that died. Even the drabbles faded away. Today we have almost a rollback to flat, simple writing, poor jokes, and small patches of stories in crossover universes. Also, as MacGeorge noted recently, a boom in OCs. It's not that we've ever lacked mediocre or poor writing; but there is no longer a continuation of good writing to offset the weak.
I've been working on comparing the hlh_shortcuts stories to both "LJ house style" and to the postmodernist trend mentioned in the OP. Sorry it's taking me so long to work on these. Concrete examples would help.