I think Hook is the only actual divisive character on the show. There are people that are not big fans or Regina, but i don’t see a lot of hatred for her. Most people like Emma, Regina, and Rumpel. All of the characters have had their divisive moments and i do see people talking about Regina having a lot of screen time, but it is not even in the realm of how upset people were with the overuse of Hook in Season 5.
I don’t think the ratings are coming back up on this show no matter what they do though. Whether Hook stays or goes is not going to matter. If they had gotten rid of him earlier the show might have been saved, but it is too late now.