If you've rote learnt an essay that was not able to meet the demands of the given exam question, then yes, you would lose marks - probably in the C range. It doesn't matter if one isn't naturally good at English, what matters is that you master the art of adaption, because to mould an memorised essay also requires an understanding of the content to some degree - you can't just rely on pure rote learning for the course. That's why you need a fall back option in the form of spare body paragraphs and/or random quotes and techniques in case your rote learn essay does not suit the question.