Lafai had the best two months of his career before his last deal, and he disappeared almost the minute he signed on. He clearly has (or had) the capacity to play well.
If he finds form again, then the issue is mental and motivational. All these guys are elite professionals who have been playing the game for decades. There isn't a great deal physically between most first graders and even where there are differences, a Cam Murray can still influence a game as much as a Burgess.
The issue, again, is coaching and leadership. There are no repercussions for playing at a standard that would get you dropped at any other club.