I don't do overarching outlines and I don't write chapters sequentially, but I still almost always begin with a list of events and notes, which then morph into paragraph headers, which then accrue more details, and so on.
Does it cease to be an outline past a certain point of detail?_? It seems an unhelpful distinction to me. In my head I regard my outlines as a kind of draft, and everything after is just editing or revising.
The projects where I've extensively used outlines, the outline goes into the draft document and then, as chapters are written, parts of the outline are deleted until there's only the draft left. (Obviously, this happens in a document separate from the original outline, just in case.)
In my experience outlines are like a second cousin to a synopsis, but usually include world-building notes that wouldn't show up in the synopsis variation. Once you start adding dialog, internalization, and narrative, it ceases to be an outline.
When I was in film school doing screenplay work we would sometimes have outlines for projects where the outline was 1/3 the size of the screenplay. But it still wasn't the screenplay. And the work of turning that 30+ pages into a screenplay required more than just slowly adding details.
However, everyone's method is different. If you find you can just add more and more and more detail and suddenly have a draft of a book, then that's what you should do. I've met more than a few folks who get stuck in that "adding more details to the outline" stage and never produce a book, and therefore, as a general rule I cannot recommend it. (That's my major concern here. I've met a lot of people who are waiting on the outline or the research or the world-building to be perfect before they write that first page of the book. And they spend years working and still never write the book because all the "source material", if you will, is never perfect enough. So, to me, telling folks that writing the outline is the same as writing the book... it's an exception, rather than a rule.)
I also suspect that even for folks who flesh out the outline until they have a draft, there is a point where most would - if they really thought about it - recognize a shift in the way they are approaching the material that leads them from "really detailed summary" into "narrative prose".
Aggy, seen many a world-building binder in her day