This is sort of like the question of whether a tree falling in the woods makes a sound if there is no one around to hear it (or something like that). If there is not a strategy provided to the creative team, or the strategy is bad, what happens?
The answer is: the creative team will develop the strategy in the work they present. By writing headlines, by doing layouts, by creating work to present, the creative team authoring the work also authors the strategy. They may not know it. But that’s exactly what they are doing. By writing a headline that says – “A new product from the brand that brought you XYZ” instead a headline that says – “Our new product does this,” they have decided the competition, the audience situation, the benefit and the reason why.
And that’s exactly the reason why a strategy should be developed to guide the creative. Not that it should be done without their input; I’m a big believer in creative participation in the development of creative strategy (if they don’t own it or feel they can work well with it, the strategy ultimately just be a piece of paper that sits to the side).
Besides, I’ve learned that creative people actually prefer working with a strategy. Oh, they may gripe about it at times: too confining, they don’t understand it, etc., etc. But they prefer having some direction rather than a blank canvas. They want to think about how to bring a strategy to life. Not about what the strategy should be. And if you don’t provide them with one, deciding what the strategy should be is exactly what they will have to do.