Holy shit, I can't believe how badly Bob missed the point about Luke. Luke lost the fight against Vader because if he won then the villain of the series would have effectively lost his balls. It was meant to establish how powerful Vader is over Luke. George Lucas wanted about three more movies after Episode V so he needed to show how much farther Luke needed to go in order to beat Darth Vader. Not to mention, it doesn't make sense for a newly trained Jedi to beat one of the most powerful Force users ever.
As for Episode VI, Luke's entire arc revolved around him not giving into the Dark Side of the Force. Vader wanted to kill the Emperor too, and he tempted Luke into joining him to rule the galaxy. If Luke just cut the Emperor down he would have ended up joining Vader. This is literally the entire point of Luke's character and the movie practically beats you over the head with it.
Luke's story isn't one of action, it's one of growth from a simple farm boy craving adventure to a Jedi master who only fought when absolutely necessary. Remember, Yoda had to teach him that adventure isn't what a Jedi craves. Luke grew from someone who wanted to be a badass into someone who saw the bigger picture. It's ironic Bob is criticizing the character for not being an action hero when the point is that he matured, something Bob never did.