Basic stats + watching any Ducks game is enough for anyone to realize our defense is under-performing. I'd argue half the defensive coordinators in the country could get more out of our defense than we are right now.
I think the perception of our defense would be entirely different had we not had such horrible O-line issues.
With the offense at full strength, our D was great for the MSU game. After that, when the O couldn't stay on the field, the D struggled... and is anyone really surprised by that? You put any defense on the field long enough, and eventually cracks are going to start to show. That's why people still value stats such as time of possession.
We have looked better over the past three games though... and, not surprisingly, those improvements have coincided with the offense getting its groove back.
Another thing to consider is our LB corp. Everyone here seems to agree it's pretty bad. Who's to say that other DCs wouldn't do worse trying to cover the weaknesses of this unit?
EDIT: One more factor to consider: Arik Armstead. He was HUGE in the UW game; he was also HUGE in the Arizona game. Remember, AZ barely moved the ball in the first half, but as soon as he went down with injury, AZ ran through his side of the line again and again and again. Cal and UCLA also got big yardage on the ground with Armstead out (although total yardage wasn't much of a factor defensively in either of those two games, with the D getting plenty of stops/turnovers for easy wins).