I think that instead of banner balance that all of the teams are connected to factions/strat relations. For example, lets say Hero Party and Occitan are at war. If they join a game (battle or siege) they would be on different teams and for their allies have them be on the same teams. Now, I know that you are going to say well, what if a faction is allied or against on both sides? Well, then have the players in the faction in question be randomized on different teams. But have the people on the same factions on the same team. In order for this to take effect, have place on the website/forums to click on the faction and if both parties click a box for War and Peace then Allied, and than for neutral. To become neutral both parties DO NOT have to click it, only one of them. Also, a box to click that says at peace and neutral with all to save hours of clicking each box.
P.S add Final bosses heirloom pack and heraldic horses and lances!