The claim that a triumphant will is all it takes to overcome it

No, the claim is that people have enough knowledge and access to information that they can debunk any piece of propaganda they see, but they make the rational choice not to and instead go along with it. This choice is not some free will idealistic choice, it happens due to the material conditions in which the people live and the social purpose of propaganda which lets them easily justify their dominant global position as a westerner. The point is that they don't have an actual excuse for "believing" propaganda, but that they go along with it mostly because they want to keep their privilege (or see it as a way to get some), even though on some level they know it's a bad thing.