You're right, that using deepfakes would be difficult to manipulate the general public with. There are plenty of dangerous cases where deepfakes could be effective, especially in the military or in business. The article sites two examples:

what if you see satellite images of a country mobilizing or testing nuclear weapons? What if someone synthesized sensor measurements?

Another example I could think of is a highly sophisticated spearphising attack. What if someone impersonated a boss's voice over the phone? What kind social engineering/manipulation could that type of adversary get away with?