Well it depends. Generally, writing more words means you're getting more content in. It's pretty difficult to get the amount of depth required in a 10/10 text response without going to at least 1000 words, if not more. I wouldn't say that a long word count is a requirement of a 10/10 essay, but rather more of a common consequence. However, it's still possible to score well without it if you happen to be really concise.
Looking at it from the other side, I actually believe that a 10/10 on language analysis is definitely achievable, and perhaps even more achievable with a low word count, perhaps 700-800 words. Excessive content in a language analysis often leads to the analysis of worse examples, which leads to worse analysis. The point of a language analysis is just to indicate that you have the skill to analyse. I don't believe that analysing a dozen techniques achieves this purpose any better than if you analysed a lower number, and as I said before, may even be counterproductive. I know that many people disagree with what I've said here as shown by what played out on the English forum some time ago, but it's what I've seen from my experience.