Ballista:
I don't think this qualifies. It's not used so much to kill people (no artillery weapon on the open field is) as it is used to force people to either be killed or (critically) spread out to dodge, and to attack you. And when an army is charged by fifteen thousand screaming barbarians/heavy cavalry in tight formation, it's like being hit by an avalanche. Similarly, charging an enemy that is in tight formation gives them the chance to hold their ground. But when artillery is in play, it can break up tight formations, giving the advantage to the force with it.
Ballista: I don't think this qualifies. It's not used so much to kill people (no artillery weapon on the open field is) as it is used to force people to either be killed or (critically) spread out to dodge, and to attack you. And when an army is charged by fifteen thousand screaming barbarians/heavy cavalry in tight formation, it's like being hit by an avalanche. Similarly, charging an enemy that is in tight formation gives them the chance to hold their ground. But when artillery is in play, it can break up tight formations, giving the advantage to the force with it.