I think a big part of the problem is that both of these things were going on, and most of the change came during season two. It was in 2B when Snow started alternating between hope speeches and despair, and those two beats were hit over and over again for the rest of the series. I think most of the Snow storylines, whether in flashback or present-day, were either about her despairing and being taught to have hope or about her choosing not to do the most appropriate thing to deal with the situation because of some vague idea of hope that some better way would come along. It was in 2B when they started having Regina be super evil in the past but a misunderstood victim in the present, and that was the only beat they hit with her. Even the Robin relationship storyline ended up boiling down to Regina as misunderstood victim who just can't win. Belle's downfall came earlier in season 2, when she saw just how evil Rumple had been and still was and yet she was still championing his good heart. That kept getting reset every season, when she'd be angry at him for something he did, break up, then come back to him, only to be shocked when she discovered that he was evil again. Rumple was seriously ruined in season 4 when he went off on an evil spree about five minutes after giving his heartfelt pledge at Neal's grave to do better, but I think the seed was planted in season 2 when he found his son and it didn't seem to matter at all to him. He no longer had that excuse for his actions, but he got even worse, and he pretty much ignored the long-lost son he was reunited with. Henry was ruined in 2B, as well, when the other characters stopped challenging his childlike declarations ("heroes don't kill!") and when he didn't seem to be all that bothered by what Regina and Cora were doing. Basically, 2B killed the series and most of the characters.
Emma didn't get truly ruined until season six, but the problem was that they just kept hitting the same beats. Every season she would struggle with her magic, have a big breakthrough of believing in herself, then be able to do anything. They supposedly solved the WALLS problem in season 5, but then they're back in a few episodes. I find it utterly bizarre that they took a character whose main issue was a tendency to go it alone and not trust people, and her Final Battle and climactic moment in the series required her to face her enemy alone. Emma's big victory should have involved a group effort, her calling on the others for help. That would have demonstrated how different she was from the person who came to town in season one, and it might have provided a twist in the prophecy, rather than it just playing out exactly as we saw, like if she realized that the problem was that her friends and family were just standing by in the vision, and the way to change things was to get them involved.
While they didn't actually ruin Hook, I think the problem with him was that although he'd changed so much internally and he went through so much, the character didn't actually change. He did the right things and usually said the right things, but they changed as little as possible about him -- same wardrobe, same piratey regalia, still carrying around the flask of rum to sip from in moments of stress (which gets uncomfortable in retrospect since they depicted WHook in season 7 as an alcoholic who stopped drinking when he turned his life around). We'd seen him change his life a couple of times in flashbacks, and in those instances he changed everything, so it makes little sense for him to perhaps make the biggest change of all without really changing.
I guess that's another problem, that there were a lot of mutually exclusive things going on -- Snow is the pessimist who gives hope speeches. Regina is the super-powerful queen/mayor who's an underdog. Rumple always chooses power and does evil but he has a good heart and Belle is right to believe in him. Emma is wrong to have WALLS and always go it alone, but dealing with the current crisis is her sole responsibility as the Savior and she should sacrifice everything for others. Hook is totally reformed and has renounced evil, revenge, and darkness, but he can't change anything else about himself, like the way he dresses, talks, or acts.