No one actually wants banner balance turned off no matter how hard it unbalances the game because people want their multiplier. With BB one can at least hope to be autobalanced to the "clan" side (or the goodclan side if there's more than one) and expect a decent return on XP. Without BB and with actually fair teams neither side gets a multiplier and no one wants to play, which is why CRPG is one of the only competitive multiplayer games where it's common practice for the balancer to place a full set of preformed players onto one side and a full set of randoms on another.
Much like many other aspects of this game very few care about balance, most care about maximal personal gain.
It's as much a side effect of the XP system as any other factor though.