I feel your frustration; we’re aware that the documentation needs improvement. See e.g. here:
there are probably some other responses in that thread you may be interested in, in case you want some more context of the existing discussion.
Re the “in the near-ish future” in the post I linked: the plan is to migrate the docs themselves to Typst, which requires some more work on Typst’s HTML export. Once these two steps are finished, I’m fairly confident that doc improvements will come more into focus, maybe/hopefully also in terms of community contributions.
Re your concrete criticisms:
I assume you have seen Formatting – Typst Documentation; do you see any specific things missing from it? I’ll add a first thing: the only show rule there is for text, which is not even recommended most of the time (this is addressed on the next page of the tutorial though), and there’s no show-set example, even though that’s super important in practice.
Functions in general are at Scripting – Typst Documentation, but yes, a detailed description what modifying a variable in Typst can and can’t achieve is necessary.
fwiw, the shortcomings mentioned in the previous thread were as a consequence reported on Github and promptly improved, so if you have concrete suggestions, please bring them. And if you have concrete questions, please ask them here on the forum.