That is why each new film from the original, things always were stepped up a notch.
ANH had our first lightsaber battle – between an old man and his older former master.
To RotJ we had a battle between an older sith lord and a jedi yet to come into his prime.
Then to PM, where we had a lightsaber dual between force users where for the first time we knew one side or the had to be killed.
Onwards to RotS, where we had two at the height of their powers in the force.
So if in ANH they had upped the combat between Vader and Kenobi, just imagine how that would have effected the films after them, and how truly fearsome Vader could have been.
In ESB, where it was revealed Vader himself had a master, just think how much more we would have feared the Emperor if even the Big Badass Vader of the reimagined scene still knelt down before him.