In the Death Star fight between Obi-wan and Vader, there's one wide shot where they do a really fast back-and-forth. That to me looked like the most realistic depiction of a lightsaber battle. But in all three OT swordfights, there was always one participant who didn't want to end it. In the Vader/Obi-wan fight, Obi-wan didn't want to be aggressive, and it didn't look like Vader wanted to kill him. In Luke/Vader on Bespin, Vader was clearly toying with Luke. And in Return of the Jedi, neither Luke nor Vader wanted to kill the other, so I can understand why the swordfights were slower than in the prequels.