You're wrong in comparing LLMs to a spell/grammar-checker (Syntax v Semantics) If LLM is a tool so is a ghost writer (not)

You're probably extending the logic from the idea that a programmer-llm is a tool. That is at least a defensible position. A written program isn't written to be experienced by people (usually), rather to create certain outcomes.

On the other hand, the written word is the entire experience of the person reading your thing, and that can all be created by an AI without your input. It has it's own biases and motivations and "alignments" (so to speak). Thus it is not a tool and actually a writer itself. And when it writes, you miss out on the experience of having written it, thus actually you end up becoming the tool (pun intended) that LLM is using to express itself.