The driving guideline behind discoverability in a ribbon (and to a lesser extent the Settings) is to balance a combination of the most common tasks and the most powerful ones front and center. The answer to "Where do I go if the thing I want isn't on the ribbon?" is sometimes "Maybe there's a more common way or a more powerful/capable way to do it" because sometimes "it's no longer meant to be discoverable". (Though sometimes its simply it was underestimated to be a common need, maybe because its primary users opted out of telemetry.)

Personally, I think most of the ribbons are extremely discoverable, but obviously your mileage may vary. I agree though that the search boxes for ribbon functions should offer a "teach me to fish" moment of maybe somehow helping you see how you missed that option in the ribbon. Office at least uses the same icons consistently between search and the ribbon so you could potentially get used to the landmark and eventually figure out the sign posts along the way (and Help documentation still exists and is also in the search results).

> I wish they'd spend less time paving paths they can think of, and more time improving systems for discoverability that also address all the things they haven't thought of / haven't prioritized.

The Ribbon (and most everything else in this post-Ribbon era) was extremely influenced by user telemetry to figure out what users were actually using day-to-day. It was designed in coordination with user studies to observe how to make it as discoverable as they could. It didn't just come out of thin air in some ivory tower specification, it was prioritized as much as anything else by telemetry from users.

Similar for Settings, I'm sure the things that are moved into the new application and out of the old Control Panel are being prioritized by telemetry. It never surprises me that the users that most often complain about their "favorite" most commonly used settings not getting migrated most often don't have telemetry on.

I'd say the Office ribbon is still sort of hierarchical, just laid out differently. tab -> section/group -> item -> submenu/subdialog.

If something isn't on the ribbon or in any of the subdialogs it's almost certainly because it's deprecated and only still exists for some obscure compatibility reason.

As for Windows Settings, it's unfortunately weird not for some principled or philosophical reason, but just because they're still not done reimplementing all the features and use cases they want from Control Panel into the new framework.

In spite of my nitpicking I agree with your general point.