Very well done. I really only put up with the rest of the movie to see Luke fight Vader, so this edit’s a blessing. I only have two problems, and one of them it seems you’re aware of. It may technically break the philosophy of this edit, but perhaps inserting a very small clip of the space battle, between the two scenes where Luke jumps to the window, would work.
“I’m afraid the deflector shield will be quite operational when your friends arrive.”
Cut to battle outside, just enough to make it clear that things are not going well and that the deflector shields are still up.
Cut back to the throneroom.
“As you can see, my young apprentice, your friends have failed…”
My other minor complaint is that when Luke first grabs his saber, it seems like he goes directly for Vader. I tried something similar to this edit once, it didn’t pan out, but I do remember that I had Luke go for the Emperor’s neck with Vader blocking, just as it happens in the unedited movie. Directly following that was a backwards clip of the same clip. So it played out like this; Luke tried to kill the Emperor, Vader blocks, they lock blades for a bit, then they lift them away to begin fighting.