Indeed. Klitschko totally underestimated Fury and payed for it. But it was an one off. It is like judging Buster Douglas based on him match against Tyson, or judging Hasim Rahman/Oliver McCall based on his match against Lewis.You're picking one fight out of his entire career and disregarding everything else. It's like watching Heskey do step overs and saying he schooled the football world. Being great once doesn't nullify everything else you ever did.
In fact McCall might be a very good comparison. Both McCall and Fury had the match of their life while Lewis and Klitschko had the worst match of their lives. And then both McCall and Fury suffered depression after that and never came back as strong.