I don’t really think how evil Hook and Rumpel are is relevant to the conversation. I don’t like either of those characters and they didn’t have redemption arcs, but neither did Regina.
In Season 1 Regina murdered Graham because he remembered and Henry knew it, so he didn’t spend time with Emma for weeks because he was afraid Regina would murder her. Regina tried to murder Emma, and, instead, Henry almost died from the poisoning attempt. In Season 2, Regina kidnapped Henry by threatening to kill people in the town, so he went with her. He tries to leave and she uses vines against him just like her mother did to her. Regina tells Henry that she is going to use the fail safe which will kill everyone in town and take Henry to live with her. He doesn’t like this, so she erases his memories. Regina constantly neglects Henry throughout the first two seasons. Regina constantly through both seasons suggests that other people’s behaviors are the reason she does evil things, saying it is their fault that she is trying to kill them. She constantly expects Henry to be the one to keep her in check even though he is a child; he constantly has to talk her down from murdering people.
The threatening to kill family members to get a child to do what you want is classic abuse. The neglect is also classic abuse. The emotional abuse is also classic. I am not saying Regina doesn’t love Henry. I think Regina does love Henry in the only way she knows how in those early seasons, but that doesn’t mean she wasn’t also abusive.
Regina’s behavior in Season 2 is just inconsistent. The way the Emma, Snow, and Henry react to her behavior is inconsistent with Season 1. It is a writing error and it has continued to be the major writing error on the show. It started with Regina and now every character on the show is written in an inconsistent manner, sometimes a character will behave one way in one episode and then behave a completely contradictory way in the very next episode with no foreseeable reason for the change. It is bad writing to the extreme.
They could have written a redemption arc in Season 2, but, in my opinion, they did not. They just flipped a switch. One moment Regina is the villain, who cast the curse and tried to kill Emma and instead Henry almost died. The next she is my mom, we have to save her, she’s not dying. Then Regina continued to waffle back and forth throughout the season, trying to murder Emma, Snow, Charming, and general townspeople, joining with Cora, almost casting the fail safe, but then being invited to parties at the diner or being asked to babysit while Henry is in his sleep curse dreams. It is just crazy and Regina is a character, so it has nothing to do with her, it is just writers, writing very, very badly.
I, actually, like Regina too, for a lot of the reasons you said, because she does in later seasons become part of the group. She teaches Emma magic. She co-parents with her. Regina and Snow have some great scenes even though that never was what it could have been. There is a lot of really interesting things going on with her character in later seasons and i actually really like the Regina and Cora and Snow arc in Season 2. Regina is easily the best character left on the show right now, for me, but none of the negates the fact that in Season 1, Regina was the villain and that she abused Henry. That she was so inconsistent in Season 2 and that the other characters reaction to her behavior pretty much ruined the show. Then Hook was introduced and he completely ruined the show to where it is now completely unfixable, so the writers are pretty much scrapping it and trying to start over with a new story.
I think the writers knew near the end of Season 2 that they had made a huge error during that season and tried to fix it. The problem is that they do not understand what they are doing wrong. They made Regina more likeable and had her show real care for Henry. They jumped the shark and introduced a love triangle for Emma. They made Hook her love interest and got rid of Neal. They did all of these random, crazy things in Season 3 because they knew that Season 2 did not work for their audience. The problem being that the things they did were not what was wrong with the show and they only continued to lose viewers. They lost half the audience by the end of Season 3 because they didn’t get what was wrong with their show. What is wrong with the show is that the characters are written inconsistently. That is it.