That’s not half the movie that you just described, though! Most of the general shape of the film, the plotting, was pretty similar. There were a lot of detail-level tweaks along the way but I don’t think a lot of what Abrams/Kasdan came up with during their phone calls changed too drastically once they started hammering out the script. For example, the Force-vision was different - but it was still a Force-vision that essentially covered the same ground. The saber IIRC, WAS effectively the map to Skywalker. A lot of what did get changed was streamlining and cutting, not necessarily inventing new things to replace old ideas wholesale.
They were working really fast, and didn’t have a lot of time to drastically change the shape of the plot once they laid it down. Almost all the beats are exactly the same, and it’s almost all the same people hitting those beats. It’s just a matter of shaving stuff down and compressing what’s left. The biggest addition was probably Poe still living. The biggest subtraction was probably the Sledgehammer stuff.
It’s not very much like what happened with “The Star Wars” on the way to “Star Wars” where only the vaguest shape stayed in place and almost EVERYTHING got rearranged on the way to the finish line. Arcs, relationships, plots, basic concepts…
I think Trevorrow had probably changed as much of the structure and shape of Duel of the Fates as he was going to change with that later draft we kind of know about, which is probably why he got axed, because that was as far as he could take the idea and have it remain coherent. And then it seems like the next step was him agreeing to maybe polish whatever Jack Thorne turned in when he was hired, and then him looking at Thorne’s draft and going “yeeeesh.”
I think it’s safe to say that we weren’t getting too many more changes for DOTF beyond what that later draft was. It would have had some cosmetic detailing and shifts here and there, but I think you’d have gotten (if they’d let him) something pretty recognizable to the story as we’ve read it in that first draft.