I have a character that I really like. They were originally intended to be the main villain for a particular story arc and then get killed off for good at the end, but I felt they were really interesting and had a lot of potential that wasn't being utilized and tried penciling in a redemption arc for them. The character was originally the best friend of the series' Big Good and a fellow hero before turning to evil, comes back posing as a mentor figure to the protagonist before they reveal their true colors and are defeated by the protagonist. They come off as a weird mix of Mr. Freeze (from Batman: The Animated Series), Dark Willow (from Buffy), Darth Vader, Nox (from Wakfu) and Magneto, if that helps give an idea of their personality.
I am worried about this character becoming a creator’s pet. For context, a creator’s pet is a character that the writer usually adores or relates to personally and devotes an ever-increasing proportion of the story to, often despite vocal dislike from the audience. These characters often become Mary Sues and gain increasing praise from other characters in the story, even if they don't deserve it. Wesley Crusher from Star Trek, Brian Griffin from Family Guy, and the Uchiha Clan as a whole from Naruto are prime examples of this.
The actual context as to why I am worried that my character is in danger of falling into this role is described below. Be warned, this context is kind of long...
I am worried this character is kind of "taking over" the narrative like a cancer. The overall arc of the series feels increasingly about being “the creator’s pet’s story” instead of the actual protagonists. For example, I was working on a prequel idea that was supposed to focus on the origin of the Big Good and their introduction to the hidden world, but I am finding it increasingly focusing on the problematic character's introduction to the hidden world with the future Big Good as their guide. There are reasons for this, the two have excellent chemistry and the problematic character makes an excellent foil and Watson for the future Big Good, and it's fun watching them bounce off each other.
There are easily recognizable reasons why this character is so interesting. The character has an interesting backstory, personality, and worldview, is very memorable in visual design, they are a highly sympathetic Woobie, Destroyer of Worlds, and has a number of traits that are unusual for a protagonist. For example, one notable feature of theirs is their intelligence. Being highly intelligent is seen a common "villain" trait (which is why I gave it to them), but is rarer in heroes unless it is their primary gimmick (i.e., Odysseus, Batman, Sherlock Holmes). Their potential for kindness also feels natural given their history as a hero rather than duck-taped on as with many villains with redemption arcs. Honestly they feel like they work better as an anti-hero or anti-villain than a straight villain. In some ways they come off as more original and a better protagonist than the actual protagonists, who come off as reactive, self-hating everymen (the protagonists aren’t bad characters, but they do fall into the issue of being less proactive and more average).
I'm fine with this character being the tritagonist but I don't want them to become a story tumor. My beta readers have told me they consider this character to be probably the most (or second-most) interesting character in the story, so at least there is some reason to believe it's not just me projecting my own interests onto the audience.
I am self-aware enough to recognize some of my own failings in this character potentially becoming a creator's pet. I do feel like I relate to the character more than many of my others. I don't believe a single one of their villainous actions was justified, however, I understand their feelings of ostracism enough to recognize that the plot as currently stands comes off less like "defeating the horrible monster with the power of friendship" and more of "beating up on the misguided outsider who honestly needs a hug more than being ganged up on". They're also really easy to write for. One thing I have made sure to do is make sure the character has very well-defined flaws that are treated as such and that they are forced to deal with the consequences for them.
What really made me realize there was a problem was when I wrote a short "what if" story showing what the world would be like if the character never turned to evil. Normally when there is a plot of "what if the villain was good" it comes off as shallow wish fulfillment, but in this case it turns out the character still had a lot to say and many of these things were never said in the main timeline. Their presence humanized the Big Good by giving them someone who they could talk to as an equal (and who talked back to them). They also provoked positive character development in the protagonists by acting as a mentor/parental figure, source of positive reinforcement, and positive role model (which one of the protagonists otherwise never gets and comes off as putting on a brave face for the sake of everyone else). Specifically, their comments to the protagonists on not being so shy, repressed, and self-hating come across as a lot more heartfelt because they were once in the exact same situation as them and they know how they feel (and they come off as an example of "you can take pride in who you are and not be evil"). A villain, even reformed villain, making those comments comes off as hollow because that's seen as a "villain" thing that got them into this mess in the first place. Or worse, makes the point that having self-confidence is evil.
However, making this "what if" story the main timeline would mean eliminating a lot of important moments that evoke powerful emotions and define the characters (not to mention removing the source of conflict from the arc due to them no longer being an antagonist), as well as potentially damaging some of the themes (of course, the current plot is kind of hypocritical when it comes to intended themes because of this character anyway). Basically doing so means potentially erasing the moments that made the character sympathetic and myself and my beta readers like the characters in the first place, which sounds like a recipe for a creator's pet to me. For example, this character's story is supposed to be a reality check for the Big Good, as no matter how leaderly the Big Good appears they are only human, as demonstrated by the fact that they couldn't save their best friend from slipping into darkness.
In particular, swapping the timelines completely destroys the characterization of the character that plays a large role in the initial idea for a redemption arc (who is the fourth most developed character after the problematic one and the two leads), specifically the two protagonists' daughter. This is the reason why it's difficult to just have the character ease into the role of the mentor figure after they stop being a villain. In the original plot the fact that the daughter is willing to give the villain a chance and treat them with kindness despite her parents refusing to recognize that they have changed and the daughter having her own problems to deal with is used to show the daughter has the potential to be altruistic and heroic despite being a bratty, confused teenager (and that for all the protagonists' concern they raised her right). On the other hand, the fact that the villain recognizes themselves in the daughter and goes out of their way to prevent them from going down the same path shows they really do regret their actions and have the chance to redeem themselves. The two have a really adorable platonic relationship that goes down the drain if things change. The daughter's character arc is really good and I'm afraid of ruining it. But by that point any chance the villain has to be a parental figure and mentor to the two leads and help them is long gone.
At the same time, none of the interesting character traits that they exhibit in the alternate timeline (which they are supposed to have even in the main timeline) ever show up in the original redemption arc. Instead they come off as constantly depressed and having a case of perma-PTSD over what they have done and never manage to come to terms with it. They barely even talk with the protagonists or the Big Good during their redemption arc. Even though they have a redemption arc they never seem to take full advantage of it as a character.
Honestly, the fact that I am even tempted to swap timelines in the first place to give this character a bigger role and more time to interact with the protagonists, even if it is to provoke character development, just screams "potential creator's pet" to me. I realize the best thing for me to do if I like the character is power through and give them the story they "deserve", telling the best story possible even if it's unhappy to make them more memorable, but I feel like I'm wasting potential and the story feels too depressing to write with little catharsis for the reader (which is bad). I have been trying to find a middle ground between the two plot ideas, but have had little success.
Sorry for all the additional context, I've thought a lot about this issue before seeking external advice and there's a lot to unpack. The tl;dr: question I'm trying to ask here is how do I stop this character from becoming a creator's pet?