My unpopular opinion about the first Dexter ending is that it would have been a GREAT ending if Hannah McBitch wasn't in the final season at all. It's so incredibly nonsensical how Harrison looks at Hannah as a mom when he barely spent any time with her. He spent more time with Jamie, how come he never confabulated Jamie as his mother? That would have made more sense. Jamie could have also taken Harrison with her (even if it was made clear to the audience that her keeping him would be temporary) at the end; they didn't need to bring Hannah back.
It feels like the only reason to bring Hannah back was for her to take Harrison, since they had decided to kill off Deb. The last we see of Hannah in season 7, she appeared to be scorned by Dexter and ready to get revenge (the black orchid she placed at his door was definitely a THREAT). But then she returns and is ready to play nice? Makes no sense. Also makes no sense Dexter would have been okay leaving Harrison at her care, when she could easily kill him if his presence inconvenienced her in any way. Let's not forget she already tried to kill Deb, someone Dexter cares deeply about, because Deb had become a nuisance to her in season 7. What guarantee does Dexter have she will not attempt the same with Harrison at some point if she feels he's gonna get her caught? Or she doesn't want to take care of him anymore, etc? But I digress.
My point is, there was no role for Hannah in the final season outside of becoming Harrison's mother, since the role the show wanted to fit her in was already taken by Deb since the first freaking season. And if the show's PTB would have allowed Deb alone to fulfill that role in the end, even if they killed her off at the end of the series, the ending would have been actually quite solid (as much as I HATE that they killed her off).
Since the first season we had hints toward Deb being the person who makes Dexter realize he does in fact have regular human being emotions. THAT was Deb's ultimate role when it comes to Dexter, along with Rita's, along with Lumen's, along with Harrison's roles... A role they ultimately decided to give to this bland and late-introduced character of Hannah McKay. The show acts like Hannah did that for Dexter, when the catalyst for this realization (because personally I do believe Dexter always had the capacity to experience these feelings all along) was RITA. It's so annoying how the show treats Hannah like this life-changing character in Dexter's life, when he already knew he could experience love through Rita, when Deb has been there all along, when he already knew he had empathy and compassion when helping Lumen... All of them already showed Dexter he's more than just a dead-inside psychopath. But yes, the one who ultimately was meant to play this role in its most powerful expression in this show, in Dexter's discovery of his own self as a person with a complex range of emotions, was indeed Deb.
Whether you see her as his adopted sibling or a romantic interest is irrelevant, the first episode of the first season establishes Debra as the catalyst to Dexter's realization of his own humanity and the depth of his capacity to feel. Dexter says in the first episode: "I don't have feelings about anything, but if I could have feelings at all I'd have them for Deb". This line alone establishes this theme for the series. So an ending in which Dexter realizes his own capacity to feel things through Deb would have been ideal. Even when they chickened out of the romantic plot after season 6, they could have still gone with this theme and completed the story thread that was woven into the show since the very first episode of the very first season. And if they had to kill her off, then an ending in which Dexter understood he was the common denominator in the disgrace of those he loves, and decides to take his life after the loss of Deb, that would have also been a better ending. Tragic, but solid. An ending that made sense. Dexter jumping into the water after Deb and that being the end would have also been solid. But, like I said, if only Hannah's presence wasn't a thing in the end. Because Hannah muddies the waters. Because she detracts from Dexter's motivations to do what he's doing at the very end. Because, again, the show made is so it was Hannah's presence in Dexter's life that which enabled him to become aware of his own humanity and capacity to feel love and his want to be more "normal". They made it so Hannah was the one person with a magic touch to turn the wooden boy into a real boy 🙄. A character that meant so little both to the audience and to Dexter's story in a broad context.
Tl;Dr: if Hannah wasn't there, and we still got the same ending in which Deb gets killed and Dexter decides essentially to commit suicide by driving into the hurricane, and ultimately failing to kill himself, that would have made this terrible ending into something more digestible when taken in the context of the story that was being told right up until the moment Hannah shows up in season 7; a story in which Dexter becomes aware of his own humanity and capacity to feel, and his own reality as a killer ("I destroy everyone I love"), through his relationship with Deb and his love for her (again, whether you want to see them as adoptive siblings or in a romantic context).
