They had him in LF in the minors. They have Wallner in left, he's not going anywhere most likely, unless they don't bring back Kepler and move Wallner to RF. Also, Martin is likely to be a MUCH better LFer than Julien, much like Lee will be 2B......so if you move him for Lee, do you move him for Martin? That said, yes, Lee will field much better, but will he hit like Julien? If Julien had played all year, he'd be a top 5 or so 2b in fWAR, even with his bad defense......
Why are people so opposed to Julien being the full time DH, if he hits like this?