Hi just a thought I'd had about the auto-balance on the servers. I don't know if the strength of the opponent is calculated when determining the balance, but I don't think much calculation takes place other than to measure kill/death ratio.
A better system might be to assign each player an ELO rating, and then grant points for the quality of the player that they fragged. Most people play with the bots on the lowest difficulty (the default setting), so they're typically rubbish, but I think the kills/death calculation doesn't take this into account, so a bot kill is awarded the same score as a player kill.
You might already be doing this, or something similar, but I reckon if you were to calculate a more accurate score with ELO or similar you might be surprised at how the team balance changes. Of course, no system is perfect, but I reckon you'll get a better approximation of true player ability over a season, which would then inform the auto-balance more accurately.
Just a thought