Maybe it's my rose colored glasses, but if Justin gets close to a ball, I presume Jason makes the play. Justin isn't a slouch in the speed department, but Jason reads the ball better off the bat and takes better routes to the ball.
More than a lot of things what this team needs before next year is Justin to spend some time in LF so he can learn the different angles properly. He once was a good (or at least average) defensive RF obviously the skills have slipped (he used to be faster) he should be at worst an average defensive LF, personally if he puts the work in to learn the angle tricks of LF he should be a solid defender out there. Hopefully Fredi can talk him into learning how to play LF better and get someone in there like Langerhans or someone who was a really great defensive LF who can teach him the finer points he needs still.