Yeah, individual +/- is a bad stat, it's good for 2 and 3 player combos. It tells you little otherwise.
JSJ is worth a few loss a year if he grows. Missing opportunities is part of the game. I like that he taking them. Growing his role. We are lucky to have him. If there was a system in place I say let the system work. The machine is better than its cogs. He is a team player who needs team support to play. (Reed is the same way). His function is not hero style basketball. High end role players playing with in themselves when used properly will win most games. A higher end functional player is all JSJ needs to be.