In the second trilogy of Star Wars (the more recent three), the swordsmanship of the actors is great. There's lots of aerobatics and fast swordplay; generally impressive (albeit sometimes over-the-top) performances.

But in the first trilogy, Luke Skywalker's swordsmanship appears to be an aimless, desperate swinging motion in nearly every scene. He flails the lightsaber back and forth like a wild boar. It's astounding that Vader didn't quickly put him out of his misery.

Here's what I mean: https://www.youtube.com/watch?v=KQxKOlrfZKc

Is there some sort of explanation as to why Luke's skills are so poor? Does it have to do with the story element, or is it to do with the film itself?