There is a simple way past this whole problem. Just ignore all the continuations and look at Star Wars as a stand alone movie. Sure, Empire is good, but without the proper finale to live up to it, it all fell kinda flat. Star Wars has a complete story from beginning to end and the only loose ends that get taken care of in the later movies are loose ends created by the later movies. The only major loose end left unturned was the fact that Vader was still running around, but Vader was more or less just a big hit man guy in the first film. Luke hasn't been trained to be a Jedi yet sure, but the full concept of what it even means to be a Jedi isn't really established until Empire. And as far as the rebellion goes, in theory, the whole conflict could have been over right there at the end since the Death Star was really the only trump card the Empire had up it's sleeve to dismantle the Senate. Remember that the guy said that is was impossible for the Emperor to maintain control without them, to which Tarken responds that it will be the fear of the Death Star that keeps them in line. So no Death Star, no fear, no Tarken, no control.