The only FWD JEE was better than for the entire season was the 12/13 FWD combo of Brown/Hendricks. Even as far as centers go he was low on the list: Staal, Koivu, Coyle, Granny (who I hate as a center), Fehr were all better than him. Kunin (imo) looked better than him too as the season ended, but it could be a coin flip between them. JEE was better than Rask, but that's not saying a whole lot.
You can blame his linemates, but he played his best hockey when he was on a line with Foligno. Straight north/south hockey without a lot of thinking involved. He doesn't process the game fast enough mentally to play more than the grind game in the NHL. He's young so there is still time for everything to "click" for him, the learning curve is different for all players.
I do think he needs more stability in his linemates. A season, or a chuck of it, on the 4th line with Foligno and Hartman might do a lot for his game. Let him get good at the simple things before adding another layer to the game. He'll still get his scoring chances on the 4th line, but he needs to pot them. He's had like a 5.5 s% over the last 2 seasons; that's not good enough to be more than an 11/12/13 FWD in the NHL.