League of Legends faces the same problem that many team-based online games have: other human beings. You are playing 5 vs. 5, and what are the odds that you can get 10 random internet people together without at least one feeding (intentionally or not), trolling, griefing, leaving… at least cheating, hacking, and glitch-exploiting have not been problems I have run into, despite their prevalence in other games. Even if everyone were trying, I don’t know how well the system does with balancing teams. The mix of newb and pro on each team often leads to some kind of balance in the aggregate, but then you have the apocalyptically awful as well as smurfs.
My rage of the day is simply getting a 5 vs 5 game going. Of my last 6 games, 1 had no disconnects. (Connectivity seems to be a commonly observed problem.) Some of those were against bots, so we had 4 vs 5 despite only have five possible points of failure. Even the bots are pretty rough in a 4 vs 5 fight.