In my opinion the corect team balancing can be just if you count the number of kills from each team and after moving one or more players, the kill will be almost the same. For exemple if Red team have 3 players, and Blue team have 1 player, and the score looks like this:
1st player from Red team: 20 kiills
2nd player from Red team: 10 kills
3nd player from Red team 3 kills
1st and only player from Blue team 9 kills
The correct option for real balancing is to move 2nd player from Red in Blue team, then in Red team will be two players who will have 23 ( 20 +3 ) kills togheter, and in Blue team will be also two players who will have 19 ( 10 + 9 ) kills togheter, and that can be more fair play. Now this auto balancing system always move last player, then in Red team will be two good players with 30 kills and in Blue team will be two players with 13 kills, and that's can be fair play.