Empire didn't contradict Star Wars? What fan edit are you watching?
The opening crawl establishes by way of an omniscient narrator that destroying the Death Star will restore freedom to the Galaxy... except Empire proves that was a lie.
Luke's father was a great Jedi and cunning warrior who was betrayed and murdered by Obi Wan's apprentice Darth Vader... except Empire proves that Obi Wan is a liar and Luke's father is Darth Vader.
Thus begins the path down which even the sub-title "The Adventures of Luke Skywalker" is proven to be a lie since Star Wars was really only Episode IV in the fall and rise Anakin Skywalker.
There is nothing about Empire that is "unavoidable" from what came in Star Wars. In order to be true to what was in Star Wars, most of Empire would be impossible. Only by retroactively undoing things and making Obi Wan into a liar is Empire possible.
And even as great as Empire is, it doesn't END-- but that's another issue.