Why are the essay structures for sample answers in the Cambridge past papers books different from the structures on the Writing course?
There are many ways of writing a Band 7, 8, or 9 essay. However, Chris has shown you exactly how to do this on the course so I would strongly recommend that you follow exactly what he says as it has been tried and tested.
If you try to invent new or different ways of doing it, you're not improving your scores or using your time effectively so try to use your resources to focus on your weaknesses and the things that will improve your scores.