Their intention is to do a lot more things like the imperial invasions but on a much grander scale and if people can't help each other in combat the system won't work. Thus you need to rework the system from the ground up. Remember Hamlet Defense concept? Now imagine 500 imperials washing over the town. Your not going to be able to beat that alone or even in a single party.

And think about multiple party Raids. This new system will make that very easy to implement with the simple addition of the lotting system everyone has been begging for.