There are moments where you can see why Perry was a #1 pick. He's got very good acceleration straight ahead when he is free to track someone down. He appears to have above average strength for his size. However, his biggest weakness as a LB is that he just isn't particularly agile laterally or in pass drops.
If he were a pure 4-3 DE, that probably would be his best position but he's in a system where he's slightly miscast. I think the Pack hoped he would figure out a way to improve his lateral agility and pass drops, and he has to a point, but his injuries have held him back at least a little bit.