The simple fix is player rankings and then when making random groups for Pantheon or skirmish it would group you with people close to your own ranking.  This will help limit the frustration people have when playing people that just out class them.   This is really important in this game since the way it plays out once you start losing you just keep losing.  And most people know when they have crossed that point where there is no hope for them to win so they just quit.

So if players tend to play agains players of there own skill it should tend to limit games where people are just out and out quiting midway into a game.

For a good idea of how to set up a ranking system for people that don't know how this might work check out the Elo rating system.