If you think about this the ST could have been salvaged with just a few changes:
1) Make Ben Skywalker the main protagonist of the 3 story arc, the story should revolve around his growth as a jedi, If you do this small change it fixes so many issues (see below)
2) Have Rey be the main antagonist, the emperor's lost daughter via his clones son or his granddaughter whatever pleases you. Rey Murders Han Solo instead of Ben sending ben into an angry frenzy this is the first time his emotions have been truely tested as a jedi. luke has to calm him, teach him, remind him of the ways of the Jedi- ben listens to luke he does not allow his anger or hatred of Rey to consume him, he grows even stronger as a jedi. Unlike anakin, his grandfather he was able to reign in his emotions after losing his father when Anakin could not after the loss of his mother.
3) As a child he was protected, shielded from any dark forces by his powerful uncle and his loving parents. Their love and kindess prevented the darkside from corrupting ben. Rey had no such love growing up, so she was easily seduced to the darkside- pulled to it even as if it was part of her dna
4) Dont have the emperor come back unless you plan on explaining his return EG how he survived what his goals were have this planned out thru the 3 movie story arc. The explanation needs to be well thought out so it does not diminish anything the heroes did in the OT. If you cannot do this just use Rey as the main villian just dont have Ben kick her ass 2 times so she never posses any real threat too him.
5) Keep luke around assisting and Training ben and going on adventures with him, maybe have luke fight a few higher powered sith before Ben is ready since its still too early in the training (part 1), part 2 can expand this relationship and Ben's growth as a jedi, then in part 3 have Rey kill Luke using some sort of trickery so that it is not implied he was overpowered. Final Battle ensures with or without the emperor (depends on #4). Maybe adds some inquisitors or other darkside users so ben has a few tests and people to fight instead of just fighting rey all the time lol
6) Keep Rian Johnson in galaxy far far away from star wars sets- Carbon freezing would work nicely on him, then display him at museum of failed directors who ruined franchises