Glove the caliber of Johnson? News for you, Mr. Stuck-In-2005, Johnson is a below average fielder since he came back from major leg surgery last year. LaRoche is slightly below average, but that's about the same level Johnson has been at since he came back. He's still got a great on base approach, when he's on the field anyway, but I don't see a big difference between what's left of Johnson and LaRoche.
As for laRoche's SUCK, you might tell that to his OPS+, which has literally never been below 100. *coughunlikeJohnsoncough*