Content is important but an effective message can be conveyed with very little or no content with the right image or video in place. Content may be used to explain the purpose/function of the visual advertisement if the visual is not self explanatory.
Many times content is key in informing the viewer of a particular benefit of a product or service. Using a visual in the background reinforces that content.
If you are speaking of white papers or case studies, then the case is you do not advertise as much. Content in this case becomes more important. You are trying to educate your customer or tell them a story that ultimately places your product or service as the hero or solution. It cannot be argued though that advertising and content go hand in hand.