Well, I suppose we had different experiences. I've heard a lot more people say summons are too strong than they're too weak. I guess what I'm trying to say is that summons aren't great at either offense or defense alone, but they offer both for a relatively low commitment. Compared to shields (both the spell and items) and the ultimate spells, summons aren't ridiculous. But those things are kind of broken also, so summons shouldn't be compared to them.
