All other issues aside -- and I have many concerning the Sequel Trilogy in terms of storytelling and character development -- this is the over-arching problem for me that dwarfs all else.
Han and Leia have a terrible marriage, lose their son and have him come back to murder his dad in front of his best friend? Luke Skywalker ends his days bitter and alone after experiencing failure and mass murder perpetrated by his nephew?
THIS is what Disney saw fit to grant our archetypal heroes in their old age? After all of their risk, sacrifice and daring?
Even Rogue One -- which I love -- was Star Wars meets Zero Dark Thirty, but at least their sacrifice meant something, dark as the story was.
Or did it? Because the First Order comes along and slaughters *billions* just 30 years later, handily wiping the floor with the previous era's "heroes".
It's a cynical and nasty treatment of what was once a mythic and escapist story of straight-up heroism.
Could it have been done any other way? I think...yes. But they decided to drag these characters through hell instead. It's off-brand, ultimately disappointing and off-putting.
I expect this from Game of Thrones, not Star Wars. Against the backdrop of my real, adult life it's a trivial thing, but from the standpoint of appreciating an artistic legacy, however flawed and plain silly it was -- it's a disappointment and a missed opportunity.
I once thought as you do but if Palpatine was really the instigator of the FO and cause for Ben Solo's turn then I consider that to be a valid post-ROTJ threat and not something that's the result of Han and Leia being bad parents or Luke a dejected loser. Han dying in battle against Palpatine's forces is some of the most well known "alternate lore" of the Saga so I don't think they were out of line to allow it to finally play out.
Same with Luke going into exile. I know that it will probably always rub some fans the wrong way and that nothing can change that fact but for me at least knowing that the dark power that drove Luke to exile also did the same for Obi-Wan and Yoda makes it easier to accept. Plus if you do allow for the PT and current official canon then the same midichlorians manipulated by Palpatine himself to conceive Anakin way back when could very well be inside Luke himself, and maybe him being an offspring of Anakin means he's even more susceptible (along with Ben Solo) to Palpatine's manipulations than other Jedi would be. So that's yet another potential checkbox in the "not his fault" column.
As long as TROS ends on a spectactular high note and Palpatine really *is* behind it all then I'm totally fine with things having gotten dark again before his particular brand of evil is eradicated once and for all.