I sympathize with you, and I also wish that these kinds of players would receive some sort of penalty. At least he wasn't actively contributing to the enemy team. As difficult as it is to win a 4v5, it's even worse to try to win a game where someone is 0/7/0 at 15 minutes, since not only are they useless to their team, they've actually given the enemy gold. I don't have any great suggestions for how to fix the kind of situation that you describe (like you said, it seems like something LeaverBuster or another background tool should have detected), but I do have a suggestion for fixing cases for where the Brand goes 0/13/1 instead of 0/2/1. Considering your concern for desire to keep the game enjoyable, I would recommend checking it out. I would be interested in hearing what you think.
http://boards.na.leagueoflegends.com/en/c/player-behavior-moderation/6qUT19A0-intentional-vs-careless-feeding
P.S. I suspect that a possible source for the downvotes on your post is that there is no way for people to verify your claim that this game you described happened. Normal matches (which this game was, apparently) aren't publicly visible, so it helps if you put a link to the game in your post.
