The show is no longer about Dexter, and that should be ok...there is absolutely nothing else they can tell you about Dexter that you don't already know or wouldn't come off as forced and contrived...there is nothing else his character can arc to. His cover with Rita and eventually falling for HER and humanizing his character with Harrison was his arc...everything since...Lumen, Hannah, his deviation from "the code" is all contrived and forced to further a character analysis that doesn't need to be analyzed anymore because there is nothing to tell.
The show, really, is about Deb now, and has been since the middle of last season, and what has gone on since is essentially her character arc and expounding on her character.