It's been obvious since last year that the producers don't "get" Stannis, and somehow think it's more interesting if he's yet another ruthless schemer rather than a study in the ambiguities of having a rigid sense of right and wrong.
Martin considered a lot of timelines for Jamie and Brienne's arrival in King's Landing. At one point they were to get there not only before the Purple Wedding but before the Red Wedding; you can still see evidence of that due to an error in the finished chapter, where Tywin and Jaime briefly talk about Catelyn as though she's still alive. I imagine it'll be easy enough to keep Brienne and Jaime occupied until after the wedding.
I'm more surprised that they played out the whole Dragonstone story this year. Granted, there was no other way to give it a real conclusion, but now they have nothing to do next year until Stannis gets to the Wall, unless they invent a scene where he grinds an infant's bones to make his bread.