What are your computer specs? I see no "thinking" at all done by the NPCs. They execute their turn immediately. The problem is that when there are 100 spiders, then you have to wait for 100 turns & animations to complete before your next action, so you either sit around watching your screen for 10 minutes or go make a cup of cofee.
Might be worse in multiplayer, I've not really gotten to the big encounters in my solo playthrough.
