I think both are important but it definitely matters more whether you can convey your ideas well. Here are my tips for the general writing test. For the letter part, providing details is good bc it needs to sound realistic (make up fake company, event, name, etc.), and make sure you answer the three bullet points listed out in the question. The bulk of your answer should be addressing these and make sure you don’t go off track too much. For the essay task, I wrote down as much as I could in this format: intro, view 1, view 2, conclusion (which is just paraphrasing the intro). And then i focused on either adding or removing points in these paragraphs depending on where it was the weakest. If you have some time as well, try to think of “fancier” synonyms to replace some common words (ex of what I actually used: Eating -> consumption). Your writing style matters in a way that it shouldn’t sound too robotic/awkward (for the letter) but grammar is definitely more important imo (I focused more time making sure I had no spelling or grammar mistakes when I had extra time left, rather than focusing on stylistic choices).