One of those crazy situations where the users are all wrong apparently not the developers.
Yup, that’s exactly what is going on. 
There’s a reason all the modern editors have this feature …
Well, right off the top you’ve got problems because you are wrong about it being all of them, there are others that work like Scrivener, but you chose not to list them (or perhaps are not aware of them). There are also many others that could not be in any way referred to as an outliner, but I suppose we’ll ignore that too. I would say that much of what I could say on this topic has already been written of before, so if you really care to dig into the pros and cons of two-pane vs one-pane and all that, scroll up.
The real reason you’re looking for though is because they are different kinds of software, and to a very limited degree in the case of programs like Ulysses/Obsidian, different kinds of outliners (it’s a bit of a stretch to call them one, but the definition is broad, we’ll grant you it, even though it’s a bit like calling an email client or a file manager an outliner). To clear things up a bit, you are not pitting the same kinds of software together, you are saying one whole type of software is modern while the other isn’t. This is a bolder position to take, as single-pane folding outlines quite likely antiquate multi-pane tree view outliners (like Scrivener). Given the increased sophistication requirement of displaying dynamic data in two areas of the screen rather than one area, it’s more likely folding is the old way of doing things. But this is all a bit silly, to be clear, as we’re talking about concepts that go back to the 1970s, here. Calling either of these approaches more modern than the other, or to say one is “showing its age”, at 49 years old, while the 52 year old one is fresh and modern, is to maybe use language in a strange, somewhat squirmy way.
To me it seems more productive, and more straight-forward even, to just talk about what these different design models actually do, what their pros and cons are, and how we may use them for different types of thinking, different types of tasks, and even how we might integrate them together to broaden our capabilities across the board. This is the overall thrust of what I am getting at in the list of linked threads, above.
keyboard shortcuts… distraction-free minimalistic modes, etc.
These are odd things to state, in a list that is supposedly consisting of what Scrivener lacks. The rest of your list is a bit off as well, but I suppose I could see how one might confuse retro-tech like a “hashtag”, and think it’s more modern than a tag list (even though, as above, they would be entirely wrong, and that markers encoded into text is the old way of doing things—which is fine, to be clear, you’re talking to someone that writes with Markdown, I dig retro tech when it makes sense to).
It’s perfectly fine to state, as I have in the many posts I link to above, that it is your preference to outline directly in text editors, that you prefer single-pane outliners maybe even (though again, your examples of them only barely qualify, so maybe you actually prefer something else) and to look for software that works that way. It is also perfectly fine for someone to point out that a program is a different kind of outliner than you were expecting. It is okay for software to do and be something different than what you prefer.
You don’t have to turn it into a competition, and get all weird about “UX” and “modern” in your discourse. Just be happy you know what you like, not everyone has that pinned down yet and has to figure it out, and work their way through a few different types of programs before they get it right. Be happy, not angry! Go forth and outline as you please! We are all niche enough to be better banding together, rather than squabbling over whether chevrons or +/- signs are the more modern/better/cleaner/UX-ier way of showing leaf nodes.
Anyway, good luck.
Indeed. By the way, you might want to check Microsoft Word again. It is an inline folding outliner, and so at the very least should serve as a recent (as in a few decades rather than half a century) history lesson on the genre.