Almost all of my creature light books carry Mordok's Obelisk, less used but still useful in creature light/static books is Supression Orb. Harshforge Monolith is great in Enchantment-light books because most books use lots of them, and so on. Obviously you now have Altar of Infernia... and many terrains are good counters - Zombies hate Consecrated Ground, and Swamp fits in many books as a counter.
You are right more Conjurations boost your primary strategy, than counter an opposing one, but they are still one of the most useful card types in my view - they are more durable than many.