Best Suggestion for Balancing Multiple Kings

Add a small, stacking speed debuff to each King. The fairest way to balance attacking power is to limit attack speed.
Since most players using the king will concentrate their forces, opponents should be able to counter that strategy by swarming their perimeter with superior speed relative to the player with the king. Also, shouldn't corruption within the empire create inefficiencies in the populace who resent their tyrannical rule?
-15% additive global stacking feels about right. This gives players defending against Kings a chance to bolster defenses with production and logistics, and players counter-attacking can swarm (or ooze really) around the concentrated mass.
Since most players using the king will concentrate their forces, opponents should be able to counter that strategy by swarming their perimeter with superior speed relative to the player with the king. Also, shouldn't corruption within the empire create inefficiencies in the populace who resent their tyrannical rule?
-15% additive global stacking feels about right. This gives players defending against Kings a chance to bolster defenses with production and logistics, and players counter-attacking can swarm (or ooze really) around the concentrated mass.