That's true, but I would phrase it from a different perspective:

It's seems clear that abstract thinking in particular is greatly aided by writing, because the written text acts like a thought cache. A bit like an LLM context window which you can fill with lots of compact, compressed "tokens" (words).

Abstract thoughts are "abstract" because they can't be visualized in our mind, so they don't benefit from our intuitive imagination ability (Kant's "Anschauung"). So it is hard to juggle many abstract thoughts in our working memory.

We can also think of the working memory as the CPU registers, which are limited to a very small number, while the content of the CPU cache or RAM corresponds to the stuff we write down.

Our "anschauung" (visual imagination) is perhaps something like a fixed function hardware on a GPU, which is very good at processing complex audiovisual content, i.e. concrete thoughts, but useless for anything else (abstract thoughts).