He ran past the corner and would have been wide open if not for the safety who rotated over there after the snap, according to Holcomb. If the safety doesn't roll to Roscoe, Holcomb was going to go there, but the safety ended up drifting directly to the spot he was going to throw the ball. I just don't see where it's a bad idea.
As for the rest of your post, I can't say I disagree. I was hoping they'd have McGahee as a 1 or 2 receiving option because, like you inferenced, he's a major threat in the open field.