Eclecticism and obsession with superficialities of style historically have been hallmarks of decadent art.
This isn't really true, you know.
There actually are no periods of art where the dominant style isn't an eclectic melange of previous styles.
Generally the only reason historians of art and literature ever assigned some periods the role of being "truly creative" and other eras "decadent" was because of the gaps in the historical record available to Europeans. Any time they didn't know the antecedents for the work of a particular era, they declared it "creative". Any time where the antecedents were well documented and known to them, they declared "decadent".
It's easy to look like a great creator when all the people you stole from are forgotten.
I don't know if science fiction is exhausted or not. The problem with using the Dozois anthology to try to measure exhaustion is that its quality varies so dramatically from year to year. You pick up a copy from a bad year, and "Oh no sci-fi is dead!". But next year he could have another year like 16. 16's not that long ago, really, and after I read that one I thought we were on the verge of a new golden age.
In general I think science fiction has suffered because there no longer is an audience that can suspend belief for its former extremes. Roddenberry-type visions are no longer very credible, and neither are apocalyptic visions. When you take those away, what's left is a muddle. One exception is work that attempts to describe a post-Singularity environment, but those of course suffer from the "anything can happen" problem the article author laments.