I think the dividing line between good and great marketing teams (and product teams for that matter) is the level at which they lean on data to make decisions.
Good teams tend to use data as a crutch – a tool they lean on to make decisions for them. They have great analytics software and dashboards that track every metric imaginable. When they have a problem, they consult the data and let it tell them what to do next. They let the numbers make their decisions.
Great teams, on the other hand, still rely on data but their relationship with it is framed in a different way. They know the tools they need to use but they use the outputs as inputs for their decision-making process. Instead of trying to find answers in the data, they understand what the information is telling them and use that information in creative ways. They are able to translate numbers to understand real-world customer motivations.
For instance, if sales of a particular product are slumping a good team will simply pull the product or deemphasize it in favor of a better selling product. "Customers simply don't like this product," they'll say, "let's just give them more of what they want." While this might solve the problem in the short term, there is usually more to the story.
Great teams will take that same data and ask more insightful questions about product positioning, design, promotion and find out why sales look the way they do. Pair the data with an intimate understanding of an end user can turn slumping sales into the next star product while pushing the company's product line further.
By just following the numbers and using data as a crutch companies end up with stale product lines with a diminishing value over time. To truly get value from data you must use it to inform your thinking, not drive your strategy.