Some companies may have marketing teams of far more than 18. Here at HubSpot, for example, we have a team of nearly 100. Even so, we stick to a team structure quite similar to the structure an 18-person marketing team might use -- with one modification. Design is broken off of the Content Team, and relegated to a separate team. This might make sense for your organization, too, if you find that:
You're Director of Marketing for an agency that specializes in design solutions for small businesses. You're having trouble attracting customers, though, because keeping an agency on retainer seems like a luxury for a small business. So you decide to create some DIY design tools to help them, you know, DIY. You do some keyword research and notice about 2,000 people are searching for an "infographic generator" every month, so you decide to build one that people can use for free once -- and if they like it, they can create more infographics for free if they provide a name and email address.