Let’s take a look at grammatical range and accuracy in writing.
Many IELTS test takers think that they need to have a wide range of grammar for a high score in grammatical range and accuracy in the writing section. This is only partly true. If you have a wide range of grammar but it is not accurate then it will not score very high.
My advice is to focus on accuracy rather than range. You need to think of the reader when writing. If you are just trying to impress the examiner then you are not considering the overall coherence of the essay. Keep it concise and simple. Of course, if you have a consistently wide range of grammar with good accuracy then you are well on the way to a Band 7 or more.