Certainly the original film is a unique case for a lot of reasons (the biggest simply being that there was a completely blank canvas). But I’d say stacking DOTF up against the drafts for really any of the other SW films isn’t unreasonable. They’re all individual cases with unique factors, but they all paint similar pictures, more or less: things changed a lot.

In fact, Lucas’s work on the PT is very similar to the process JJ went through on his SW films: write a script, rewrite on set, rewrite again after principal photography has wrapped. I sincerely doubt the final product of TFA was about 70% the same as the first draft. I get the impression it was more like 50%, maybe even less. That movie went through considerable changes. We know TROS had some heft reshoots as well, though at this point it’s hard to say how significant they were in terms of story, and also how much the script changed from its inception. Of the trilogy, TLJ seems to be the outlier where really not that much was changed at all.