If he had stayed healthy, he would have had at least 10 sacks. Considering that KVN is the only OLB in Bronco's tenure to have more than Kaufusi's 7 from last season, and that Jan is the only other player to have more than 7 (and only did it once) in that time frame, it's beyond harsh to say he has underachieved without blaming injuries and coaching decisions for the difficulties he has had.

If your expectations went beyond what he has done to the point that you look at his injury and being played in a position that wasn't the best fit and still want to bag on him (which is absolutely what you are doing; at least man up and admit it), then your expectations were completely unrealistic. That's on you.