But the process is the same whether you take years or months.
This isn’t true at all. The process isn’t the same from movie to movie often, much less across multiple decades in an industry that has changed a lot.
The process now is not the same as it was in the '70s. If Star Wars was made then the way ALL blockbusters are made now, we wouldn’t have gotten to draft 4, because when Ladd greenlit it, he’d have greenlit it with a release date locked and everything would have been set to that clock. Star Wars didn’t have a clock put on it until much, much later in the development process. The clock still almost drove Lucas insane, but he got a lot of time to develop that script that is damn near impossible to get now.
It’s a different machine creators are working in. Or rather, the engine and the gears move differently than they did when Lucas was around. Lucas is partially the reason that machine now operates the way it does, thanks to his efforts in the early 00s. Comparing the script development of Star Wars in 74 to Trevorrow’s efforts in 2017 is a comparison that isn’t worth much because not only are the creatives in question pretty wildly different, but the process is also pretty wildly different now, too.