Season 2 had been my favorite season up until the amazing John Lithgow came along and put season 4 at the top of the list. I wouldn't swap the Doakes/Lundy/Bay Harbor Butcher plot for Lumen. Plus, I am not sure that the Lumen story would work quite as well had it been written as season 2. I think the writers were trying to imply that Dexter needed to help Lumen overcome her trauma in order to help himself recover from the trauma of Rita's death. I, personally, don't think it was nearly as effective as it was meant to be, but I see what they were trying to do.