Not sure how hard it would be but what if defense teams were comprised of 6 teams. Each team comprised of one hero contributed by each alliance member. It would be adventageous yet not necessary for each player to play a certain role i.e. tank, healer, buff/debuff, damage. It would create an opportunity for alliances to be able to compete with much stronger alliances because defense teams are made of the alliances strongest heroes. Matching would be based on number of players and each players highest powered hero. Offense would continue in its current way. Just an idea.