That's why I don't believe Vader post-Mustafar personally hunted down and killed Jedi. His injuries left him in no condition to do so.
He went up against Obi-Wan in ANH because it was a profoundly personal situation that he needed the final say in. He went up against Luke because he knew Luke was a total amateur.
Vader probably did some training over the years, but if he had went up against a Jedi while they were in their prime (still young, yet highly skilled), he would be toast.
The Jedi Purge is one subject where I do reject EU. That's not to say that EU can't come in handy in answering questions we have from the films. Sometimes it does so brilliantly, and others it fails utterly.