Luke, Han and Leia didn’t fail
Yes, they did.
She is the daughter Luke never had.
No, she’s not. TRoS tries to pretend like Luke and Rey had a positive, familial relationship, but they didn’t. Not at all.
As for the fall of the Republic, Palpatine had been working behind the scenes for decades to allow corruption to seep into the Republic. For the most part, that decay didn’t just happen on its own. It was largely initiated by Palpatine and other hidden malefactors. We were shown a galaxy in TPM where the well-intentioned but flawed good guys were in charge and struggling to keep under control an increasingly volatile galaxy. We see the steps of the Republic’s fall into authoritarianism. It’s not perfectly told, but the transition is more or less earned. We witness the tragedy as it takes place.
In the sequel trilogy, most of the tragedy takes place either off-screen or in throwaway sequences. There is no sense of a logical progression from the end of RotJ to the beginning of the TFA. The titular “return of the Jedi” failed to take place, and we had essentially another Jedi Purge occur off-screen. The Empire, instead of being at all diminished, is now comically overpowered. The New Republic is tossed away never to be seen again, partly for shock value, partly because JJ Abrams no doubt thought that having an established Republic be the galaxy’s status quo would be too “Prequelish.” So he threw that out and the New Jedi Order with no buildup or groundwork whatsoever. Thus turning Star Wars from a story of hope after tragedy into a depressing cycle where the failures of the past are forever doomed to repeat “just because”, and forcing the OT heroes to witness everything they worked for crumble within their lifetimes.
Han abandons Leia after the betrayal of their son, and regresses back to being a smuggler under the nose of the regime he helped found. Luke abandons his friends and family and leaves the galaxy to rot at the hands of the Dark Side because he somehow blames the Jedi for his own personal failings. Leia is forced out of the government she had devoted her life to restoring, with her family abandoning her and her son fighting for the Empire. Meanwhile, she finds herself exactly where she started, as a leader of a small guerrilla rebel force, her life having completely stagnated and the struggle to which she had devoted herself being made 30 years longer and mostly fruitless all for the sake of doing a soft reboot in the seventh chapter of a story.
That’s awful. What’s enjoyable about that?