I would disagree that the sole cause of the show’s downfall is the writers promoting CS to the exclusion of all else. Personally, I think OUAT started going downhill around Cora’s death – well before Neal’s death. There’s an assumption in there that the writers had a plan for the show, and if they’d stuck to it, everything would have been good. But we’ve discussed (extensively) here how A and E are unskilled at character development, relationship building, world building, how poor they are at planning, how they change their plans simply to surprise the fans, how they might not even have created S1 without outside help. There’s nothing to suggest that the show would have been of a higher quality had they stuck to their so called original plan (if there was such a thing) or if they had not paired up Emma and Hook. I suspect it would still have been poor and offensive, only in a different way. They may well have assisinated Neal’s character, the way they have with Rumple, Snowing and Emma. We’ll never know, and the unknown seems more appealing than the current mess. Basically, it boils down to A&E being mediocre show runners, nothing more, nothing less.
While, i do think the show would still have problems. I don’t agree that having a plan and sticking with it would not make the show better. The writers had a plan original. Neal was Henry’s father, Rumpel’s son and Emma’s love interest. That was told to Jennifer before they filmed the pilot. That was the plan and a central point of the show before they filmed the pilot. All sorts of hints were littered throughout the first two seasons, all sorts of character development with Rumpel and Emma was about that, leading to that being a big part of the show. Removing that, fails the plan.
It failed the show. The writers are bad shown runners. They threw out their original plan and were completely incapable of creating a new plan and then sticking with it. Not sticking with the plan, the character arc, the larger story arc, the world building continuity, is their problem, so i wouldn’t say that the show would be just as bad if they had stuck with their plan when not sticking with their plans, with their continuity, is the problem with the show.