Best advice anyone could give to Jarvis Jones right now - go find James Harrison and ask if you you can work out with him this offseason. Rent an apartment as close to his house as you can find. Go to the gym with him every single day. Go to lunch and dinner with him as often as he will permit. Move into his basement for a few months if James will allow it. Mirror everything James Harrison does. Ask him questions. Ask James to make you into a second version of himself.
James Harrison didn't have any of the measureables coming out of Kent State. He made himself into the player he became through long hours of hard work. Jarvis Jones can't make himself much faster or quicker. But he can make himself much stronger, much smarter on the field and develop better pass rushing moves. There is no OLB in recent memory who made more of himself with what he had than James Harrison. There is no better example for Jarvis Jones.
The only question really is - does he want to improve?
That is not necessary true. There are a lot of trainers out there that specializes in speed and quickness. Like you said, he needs to put in that extra work and seek out the ways to become who he wants to be as a LB. Pure athletic ability got him to the NFL, but now he needs to step it up and improve on the details of his game. James is a workout fiend. A lot of our younger guys, offense and defense can take some lessons from him.