One of my first tests of ChatGPT was having it write a marketing blurb. It produced a better draft that I would have (ever had) gotten from a professional agency. A bit of tweaking, and done.
Marketing strategies and concepts are more difficult. Just like an LLM can write FizzBuzz, but cannot work at a higher level. Anyway, not yet...
Some of my clients have been using AI to generate landing pages for more than a year now, and they have better conversions than those written by people.
AI can easier decide where to put money, into mobile ads, print, email campaigns and create all the content for that.
If you follow the marketing model of the book "Traction", with the idea of trying marketing channels out to find a fit until you hit a saturation point of the channel, AI is much better suited to execute this model.
Marketing strategies and concepts are more difficult. Just like an LLM can write FizzBuzz, but cannot work at a higher level. Anyway, not yet...