Well personally I've tried it with just the 2 starbases in system and they still infinite cast it...
Their fleet consists of around 8 caps, no sub caps, the computer player has been knocked out of the game, just want the world now..
They just fly around casting armistice and I have no fleets in system at all and no defenses apart from the 2 starbases...
Pretty bad gameplay tbh.
It would be better to have an anti-buff put on units rather than a cooldown on the ability. So unit A gets armistice and cannot take another armistice for 5 minutes.
I don't see how they can really justify this for multiplayer...