My issue with your interpretation of Rey in this film is at least partly connected to what you had Luke trying to teach her in FotJ. My idea would be to try and get it across that by the end she’s learned that lesson of internal balance.
The film already contains external manifestation that she’s trying to achieve it, she heals the serpent, followed by using Force Lightning. She wants to take Ren’s hand, but goes to her friends instead. She mortally stabs Ben, then heals him. Her issue is that she’s struggling and I would rather see her work through that struggle and come out ready to build a new order of Force users that isn’t Jedi or Sith, than die because she’s a failure.
Ah, but this is where I would disagree. Rey didn’t fail in her death, she succeeded. She fulfilled her destiny, just as Anakin did. Her choices brought balance to the force. This Legends theme of balance is that you cannot change fate for long, as there cannot be free will in a galaxy where this force guides things. Think to what Kreia said, “I hate the Force, I hate that it seems to have a will, that it would control us to achieve some measure of balance when countless lives are lost”. - (Star Wars: Knights of the Old Republic II) I wouldn’t say Anakin failed to bring balance to the force as he died. Neither would I say that Rey and Palpatine failed to do the same. Fixing this cycle of destruction isn’t about learning to wield a “gray” force as there is only light and dark, it’s about learning symbiosis with the living and cosmic force as you fall neither too heavily into the light’s passivity or the dark’s aggression. It can easily be argued that, as Kreia believed, the only way to truly make peace is to somehow destroy the force itself. But at least at the end of my saga, the galaxy can rest without one side in charge. There is no chance that Rey possesses the wisdom to effectively create a new order of force users along these lines. It would continue to feed the cycle, so in my edit the force is doing exactly what Kreia hated: Using its will to control people to achieve a measure of balance as lives are lost.
It could be accomplished with two pretty simple changes to the Exogol confrontation and two during the finale.
When Rey says she’s here to end the Sith and Palpatine asks “As a Jedi?” change her “Yes” to a “No.” and edit Palps next line accordingly.
Then cut the Jedi from the sequence completely.
Show Rey’s friends on the Falcon with her as it goes to Tatooine.
When Rey is burying the past on Tatooine, cut the Force Ghosts and have her say “Just Rey” instead of “Rey Skywalker.”
With the changes you made for FotJ, plus the theatrical’s concept of Rey confronting her fear, this gives the very clear impression that she’s trying to move beyond the failures of the Jedi, and by the end has succeeded. She’s supposed to be the one who has resolved the Grey through refined Jedi sight, as referenced in the TFA novelisation’s Book of the Whills quote.
However it’s your edit, and those are just my thoughts on resolving Rey’s story.
Another problem with Rey living is that in that case, then Kylo’s arc has no resolution. In my cut it makes sense for him to be downtrodden as a living reminder, a Cain-like figure in the Bible, but if Rey is still alive then Kylo’s dark pursuit of her would doubtlessly spiral the galaxy into more conflict. There’s no way he would be satisfied to leave things alone as his primary motivation has always been her. And as I explained in OP, his healing power to revive Rey and then him dying is utterly ridiculous within the bounds of Legends.
As for Ben, I’d leave him on Tatooine at the end.
This is what I’m leaning towards. Him seeing the force ghosts, then ending on him looking at the suns. Not sure if this would provide enough resolution though. As Rogue said, I am a little concerned on this ending being considered unsatisfying, but I’ll see when it’s put together.