I find that question uninteresting, because no matter where the fault lies (it's probably somewhere in the middle) the end consequence is that there is no use case where it makes sense for me to use Word (unless I'm literally held at gunpoint).

I'm either working on a document for myself or with collaborators.

In the first case I'll use markdown for simple things or LaTeX for bigger things since I can work in a familiar environment where I work most efficiently (VSCode).

In the second case, I'll work with collaborators so I will never be able to trust that a document I have sent off for reading is still consistently formatted when I receive it back. This means that any benefits of the collaboration tools (eg. review history or suggesting changes) are wiped off the table. I will have to integrate any suggested changes into my own authoritative version of the document by hand anyways. At that point I may as well work where I fell comfortable and use markdown / latex, and send off Pandoc converted word files for comments by others when it is relevant.

This is of course for serious pieces of writing, not throwaway stuff like eg. meeting notes, but for those Google docs is plenty.

IMO entirely user.

Word (and similar text processors) is a toolset. All it gives you are tools. Word lets you define formatting rulesets, lets you apply formatting rules and create rulesets from applied rules.

Some evangelists may say that "safe" text processor would only allow application of rulesets, because direct application of rules leads to "spaghetti formatting". However that is one of the powers of WYSIWYG text processors: you apply the rules and extract those to rulesets once you are satisfied with results, in an explorative way. Direct application of rules is a feature that makes Word what it is.

Now, if a user takes a document with predefined rulesets and still applies their own rules inconsistently that's simply misuse of the tool.

But what of the potential lack of a compatible toolset on the other end of this pipeline? Even embedding styles in a Word document offers no assurance the document will appear as you intend when they receive it, much less if they offer edits and comments and send it back.

I don't get your point. Since IIRC Office 2007, docx is the default format which is designed for compatibility. IIRC it allows embedding of fonts and other non-text content, making compatibility concerns an edge case. If all parties use relatively recent version of MS Office with overlapping featureset, there should be no compatibility concerns, unless somewhere in the collaborative pipeline you are departing Office ecosystem altogether.

I don't think discussion around fault is meaningful in such scenario altogether.