Another thing I have to add after thinking about this today is how Luke handled Ben. Luke's first instinct is to kill his nephew. However when confronted with Vader, one of the worst Sith Lords in history, his first instinct is to turn him back to the Light Side. So Luke wants to save his dad who he never even knew, yet he wants to immediately kill his nephew who he has watched grow up for 20 some years? That right there shows how poorly written Luke was in this. Even in the movie someone (Rey I think?) tells him that Ben wasn't too far gone to keep him from going to the Dark Side.