The weak side linebacker in this defense needs to be able to make plays quickly. Ideally, it should be a sub 4.5 linebacker. KJ doesn't have that kind of speed, but he does have incredible instincts and length which make up for that.
It needs to be a reliable, assignment correct player to man that position as they are often the unblocked player who needs to be the one to make the play. KJ is an outstanding tackler and has the firmest grasp on the LB assignments between him and Irvin.
Bruce probably isn't even a year away from being the Will. He's got the physical tools to excel but his learning curve is massive right now.