I think the question is that were Plato's fears unfounded. I don't think the question is "is writing bad", although it is framed as that to justify a carefree adoption of LLMs in daily life.
Plato’s (or rather the Egyptian king’s - IIRC) fears were not unfounded, since a lot of people do not operate this way (sadly I see this with some peers), however overall the effect could still be positive.
Writing distributes knowledge to a lot of people, without it you have to rely on a kind of personal relationship to learn from someone more knowledgeable (which can be better for the individual mentee though). So maybe it increases chances of learning (breadth of audience) at the cost of the depth of understanding?