At the time Days was pretty unique with respect to it's characters and framework. Even now, Xion is one of the only characters in the series that I can think of that had an introspective conflict and as a result we actually come to know Xion's personality and motivation better than most of the cast. She's also the only one I would consider somewhat justified in being defined by friendship because that's how she ends up developing a heart. Plus I think Days has some great imagery and dialogue so I tend to give it a pass. Is it soap opera-y? Definitely, I can understand why you don't like it.
The way they handled the 'forgotten' thing was very messy in the game, somewhat better in the manga but it should have been handled better. Honestly they kind of wrote Xion's character and Roxas' future development into a wall with that, I almost think it would have been better if Xion disappeared without the fight and spared us the accompanying climactic drama. If you've ever seen Re:zero the way it's handled between Subaru and Rem worked much better imo, but maybe they didn't know whether or not they would bring Xion back so they wanted to do something like that.
I don't really know what to say about trios. I compare KH to Naruto all the time because it's ended up feeling the exact same to me. Trios tend to start off great with interesting dialogue and development between teams but somewhere along the way it's as if continuing to interweave significant dialogue between 9+ characters gets tiresome so they just stop. Character progression stagnates in order to progress the plot. Necessary character interactions that would and should happen are scrapped or ignored. The whole thing becomes such a mess and chore to write that the side characters end up getting the minimum story interaction needed so fans can pretend they're still relevant while the main protagonist solo's the ridiculously overpowered bad guys. Do I think trios are bad? Not inherently, but I do find the Male-male-female dynamic pretty tiresome to be honest. Or at least throw in a duo once in a while to change things up or something
I would say Roxas and Naminé have also shown introspection with their conflicts. Naminé for example, summoned Sora due to her friendlessness and loneliness, and that selfishness, though understandable, brought in consequences when he arrived at the castle. She desired friends and draws because those are memories she doesn't have, that sort of happiness. She acknowledged her role in it, despite that she was forced to by members of the Organization with no means to defend herself. Once she stood up to them and refused to hurt Sora any more because he forgave her despite everything, she got bitch slapped and then used as a meat shield between Axel and Marluxia. Once all was done and over, that selfishness shone through when she sounded rather bitter that Sora picked his old memories over those in the castle. But she accepted and respected him and promised to fix the whole mess. And things got complicated from there with Roxas and Xion. Her stance had to be neutral. So now she had more weight on shoulders and guilt, so she helped the best way she could without taking a side. Coded exists because of her trying to amend. And she had built a strong enough will and confidence through Sora's previous forgiveness that she rebelled and took active agency in KH2 to continue her character development and progression to aid others. It leaked to KH3. Being that she was with another abusive adult who told her she's nothing, disposable, and never meant to exist, her self esteem still took a hit, so that's still something left open based on her lines in the Final World. She still doesn't "belong" anywhere. She's practically the saddest existence in this series.
She did evolve from being a doormat to taking charge of her situation. It's the biggest female glow up from the cast I've seen and I respect that, despite that Larxene will always be my first.
Roxas was better before Xion hijacked basically everything. His goal presented in the prologue and the memories shown within that prologue was to find himself, to find why he wields the Keyblade, and to find who's Sora. What are these dreams he's having? Basically understand his identity. This changed to also trying to get his "dead" friend back in some vengeance spiel and for things to return to normal and go back to how they were. What's troubling is that whether Xion was there or not, he would still leave the Organization, still get dreams and choppy memories of Sora, still have Axel lie, still get knocked out and put in a data simulation. Him trying to uncover the truth
should have been his storyline. Xion's entire relevance depends and derives on Axel and Roxas, which is why I agree that she's defined by them. Even in KH3, her entire return is tied to them.
Axel and Roxas were a duo, and were perfectly fine as a duo, but they needed to force in another trio nonsense in there when it wasn't asked for and wasn't necessary. Guess now it's just Marluxia and Larxene for a different relationship dynamic.
Roxas has branched out with other people, has made other connections. I wanted to see Riku and him talk about what Riku had done, I wanted a reunion with Naminé, I wanted a reunion seen with Hayner, Pence, and Olette, I want to see Isa apologizing, etc. None of that was done because he was sucked into his black hole, melodrama of a trio and nothing else.
TAV was actually better done. I don't know if it was because two of them got freed before the Keyblade Graveyard, but they had the opportunity to talk and reunite and comment on the characters they connected with. Riku and Terra finally got their own in the DLC.
But again, they are "cliques" right now. They can't expand beyond that, and in turn, it makes it tiring. As long as this continues, there's going to be no progress with this supposed "Nakama" veil they're trying to portray with the Guardians. The ending for KH3 rang completely hollow cause we did not see the basis that had gotten them to that point. Horribly handled, horribly rushed. We're just told everything's water under the bridge and everyone's happy. Eh, okay, sure.
Since Naminé is in limbo and isn't stuck with a group, hopefully they can explore her more since she doesn't have to be permanently glued to a clique and can freely travel.