LLMs have solved writing in the same way image generators have solved stock photos - if you need an image that doesn't need to convey any information other than "I have added a somewhat-related image that doesn't look obviously AI-generated to this", you can now generate such an image pretty easily. That's a low bar, but almost the entire genre of stock photos exists in service to this goal.

Likewise, there's a whole lot of day-to-day writing that mostly exists to communicate "I have written some text about this subject because I am expected or required to" and at most needs to communicate some simple information. LLMs will probably replace a lot of that writing, at least temporarily. As people increasingly use LLMs to consume that information as well, it will probably eventually be replaced by some sort of inter-agent communications protocol.