As far as I’m concerned, Lucas started messing up from the beginning. The leaked script drafts from the OT show that he is correct, he did have a story and he cut it up for ANH. He abandoned some concepts he came back to later. He like some things he was cutting and changed the story. And then once he had his story for the first film roughed out, he spent a lot of time editing it and refining it. He killed off Ben for dramatic effect.
So when it came time to make a sequel, he had to go back to the drawing board. The entire Hoth sequence was added. Ben training Luke in ANH was expanded and Ben was replaced with Yoda. In some ways Hoth is the planet side battle that was cut from the original Death Star Battle. He brought back the city in the clouds but had to change what it was. That had become the section on the Death Star in the ANH. So it went from Imperial facility to a mining facility. He created the entire Vader’s hunt as a post Death Star reaction. And of course Vader being Luke’s father. So most of TESB is created to bridge to the finale with little pieces from the original story.
Then in the development of ROTJ, Lucas brought back his original concept for the final battle. The combined battle was mostly restored. But because he’d pulled Chewie out and made him tech savy, Wookies became Ewoks and shrunk, with no less ferocity in action, though a lot less in appearance. But that didn’t make a full movie. So the rest is the continuation of Han’s capture and Jabba the Hutt and then Luke facing Vader and the Emperor.
From the drafts of the scripts, the concept art, and more, We can see that Lucas likes to change things. Consistency in story is not as important to him as dramatic impact and story. That really becomes clear with the Prequels. Sure he said he created the back story while he was working on the OT, but all he had was a few details. In order to make the PT, he had to flesh it out and see what worked with the story. Sure some things don’t line up perfectly with the OT, but things don’t line up in the OT much better.
So when it comes to the ST, Lucas was in a bad place after ROTS. All the bad fan reaction led him to call the saga closed. Plus, my understanding of his early ideas for the ST were basically, wouldn’t it be neat to have these stars come back to reprise their roles and pass on the torch to a new generation. And I don’t think there is a diehard fan out there who isn’t aware that Harrison wanted Solo to die in ROTJ. What else Lucas was thinking post ROTJ is a mystery.
So when we get to the point where he actually started fleshing out the ideas, there are some things that should have been expected. Han and/or Luke dying should have been expected. R2 and Threepio surviving to the end should have been expected. Some return to conflict and a return of the Dark Side should have been expected. Pulling from the same type of sources that he did the first time around should have been expected. What I’ve seen in negative fan reaction has largely been based on these things that are pretty obvious to expect based on what we knew being disliked. It is called Star Wars so any ST was going to have a war. That in itself means that the glorious new Republic would have an enemy it would have to fight off. That we have planet destroying weapons leads to having a better version of that to imperil the galaxy and the Republic. Luke being in self exile comes from myths.
Now the quality of the writing is very much in the eye of the viewer. My gripes with TFA are all about the writing and how it fails to craft a strong story. I feel it is more about scenes than a complete story. So I can’t say that everyone should like every writing choice made, but I feel very sure that the ST we got is based on Lucas’s treatments. They definitely dumped a lot of what Lucas had, but from our PT experience, I don’t think that part would have gone over well. I think if Lucas would have done it himself that we would be having a very similar discussion. But we would be talking about how HE screwed up the PT. We’d be complaining about who he cast, the wooden dialog and acting, how no one wanted to help him write or direct the stories, etc. I think the only way they could have gotten made with any quality was for him to sell the franchise and turn the reins over.
We would be having the same discussion about what his original intentions were, his original treatments, but then about how HE screwed them up.
I don’t think dreaming that Lucas’s own versions would be any better. And I think it is very fitting for the saga that when you look at credit for each film in chronological order, it goes from Lucas doing this solo (technically he wrote and directed the first 4 movies) to him letting go for the OT and then completely stepping back for the ST.
I am very confident that I like what we got more than I would have liked what Lucas would have done.