At one point in the beta that was going to be a feature that pitted high ranked players against more numerous lower ranked players.  I've been told by other testers since that they scrapped that.  So, as to this being a bug or a leftover feature, I don't know. 

My best guess right now is that it's a bug where the AI doesn't always take over when a player drops before the game is finished loading.

This i due to the "host" of the game kicking players before it starts, most of the time. Say its originally a 2v2, but before it starts either the host kick the ai (cause he dont like ai:s) or the player that too slow to connect "is not connected to anyone". When it starts, it will only contain the remaining players. Something funny i did once and you can try yourselves, is kick any other players when you become the "host" (you have access to the kick function) and the game will start with only you and mobs hilarious.

i agree this is a serious problem. so is the favour items, and the demigods not responding to your attack commands once in awhile, costing you a kill. however there are more serious problems taking precedence right now. (network connectivity)

If that's the cause it would be difficult to take advantage of.  On the connecting screen you can't tell what side a player is on (in pantheon) unless you've played them before.  In skirmish a player could end up on any side.  You could easily kick the guy that was supposed to be on your team instead.