Keep in mind, each is the same cost of a small squad of troops. They are not cheap.
2 of them cost as much as a lower level mage, 4 of them, a good mage.
Their saving grace is that they are reusable.
What worries me is that research of your. I am going to be blown away by some high level magic. And what will I be able to counter with? I just don’t know. Yet.
Is it going to be soul slay or mass enslavement? Shit, it could be thunder storms. Am I dealing with etherael and mistformed units that will be impossible to damage?