Burbin said:

TLJ freed this new story and allowed it to become it’s own (much like Kylo in the film), it revealed that there was no set place for these characters to fit in (much like Rey in the film), no set story ‘destined’ to play out. It opened the door for the final chapter to be something new, different and original. TRoS closed that door shut, shoving everything back into the original mold: Rey goes on to be trained as a Jedi, there is some big revelation about her backstory, Kylo turns to the light, and together they defeat ~~Snoke~~ Palpatine, which marks the end of the First and Final Order, and the return of the Jedi and the New New Republic. The Empire is defeated by taking down the ‘big bad’ on the throne again.

I feel like you’re implying Kylo Ren was set up to be irredeemable, except we literally end with him broken, kneeling on the floor in the base.

I also feel like you’ve missed the point of Rey’s arc in TLJ, it isn’t about finding her place in all this or being important in general, it’s about letting go of her parents altogether, coming to terms that, to them, she is completely worthless — reinforcing her arc of how she eventually overcomes her irrational, toxic core belief that she is worthless and refuses her lie that she is only worth something if others think she is. She only wanted to find out as to what her importance (in a good way) is so she would use it to justify as to why her parents left her on Jakku, feeding her lie that her parents truly did love her, feeling loved, to push away her feelings of self-worthlessness that hold her back and leech off her happiness.

I do feel TRoS undermined Rey’s arc by having her parents be noble people who loved her, but the idea of her being Palpatine’s granddaughter does not; when she stabs Kylo Ren, she becomes convinced that, because of a combination of her heritage and her Force-sensitivity, she is meant to be consumed by the dark side in the way her grandfather was, so she exiles herself, believing that the Resistance is no longer going to give her any validation once she turns to the dark side — Luke proves this wrong by reminding her of Leia training her, regardless of her heritage, showing that the value of others is determined by their heart, not their heritage, and convincing her to face Palpatine and determine the fate of the galaxy, showing that it is not her heritage that determines her future, but it is she, herself, who determines it.