LO is at least as functional as some other market leading SaaS word processors. LO could spin their product into a cloud application and not at all be "toast", because people in separate walled gardens no longer expect interoperability.

As for complexity, an illustration-- while using M365 I recently was confounded by a stretch of text that had background highlighting that was neither highlight markup, not paragraph or style formatting. An AI turned me onto an obscure dialog for background shading at a text level which explained the mystery. I've been a sophisticated user of M365 for decades and never encountered such a thing, nor have a clear idea of why anyone would use text-level background formatting in preference of the more obvious choices. Yet, there it is. With that kind of complexity and obscurity in the actual product, it's inevitable the file format would be convoluted and complex.

Agreed, but the point the author is missing is that complexity doesn't exist due to deliberate corporate lock in, but because the product is 40 years old and has had 10-11 ways to do just about everything it does. Unfortunately, as your case illustrates, there are still documents in the wild that depend on these legacy features. So to render with 100% fidelity, you end up in a sprawling web of complexity. Microsoft can afford to navigate that web (and already owns it). It's neigh impossible for an open-source product to do so.

> The business model is just screaming that GPL'd LibreOffice is toast.

or MS might find itself accidentally toasting themself

a lot of places (including very important MS Office customers) insist in a open document format for various reasons

if MS convinces people that LibreOffice and similar is toast because they can't afford keeping steep with the format in question because it's too expensive they also might end up convincing this customers that it's also too expensive to _them_, and try to find way to switch away from MS Office