I don't disagree with you
per se, but I do think you're exaggerating things a little with regards to just how unique Sublime Text is. I've spent a lot of time switching between text editors (more time than I really should - but sometimes procrastination trumps productivity) and here are some of my thoughts on the points you've raised:
> Brackets was only good for web (wasn't it?)
That's certainly where it excels at, but there are plugins for other languages (eg I did write Go code in Brackets, albeit only for a brief period).
> Notepad++ is, I think, quite outdated
It's not the prettiest editor in the world, but it's a little unfair calling it "outdated" when it releases updates more frequent than Sublime Text does.
> Emacs (and Vim!) are hard to learn and slowly dying off
They're no harder to learn than any other IDE. But it's definitely fair to say that there's a steeper initial curve than something that's largely point-and-click; and that they're not as trendy nor pretty so most users (understandably) aren't interested in familiarising themselves with the basics.
> Other specific editors are... specific, and thus not direct competition to ST
That's not entirely fair as a lot of peoples ST use will be for specific things.
In fact I often find myself using about half a dozen different general purpose text editors for specific things: vi for when I need to edit root owned files; Kate for general config files / text files; ST for Go; Brackets for JS and CSS; Notepad++ for editing Windows scripts; and POSIX tools (echo, tee, sed, awk, grep, etc) for automation in editing text documents.
For me, ST could easily be replaced by any of the other editors I use or some of the specific ones (eg LiteIDE). I pretty much only use ST for Go because of habit and I'm sure in 6 months time I'd have gotten bored and switched again.
My point is that not everyones usage for ST to be as diverse as you suggest. So Sublime Text is still having to compete with other tailored editors as well as the general purpose ones.
> windows only ... KDE, that is very niche compared to Windows, OSX
I don't think that many people switch between Windows, OS X and Linux enough that they need a single cross-platform editor. For most people, an editor that "just works" on their preferred platform is all they need. So in that regard, Kate and Notepad++ are just as viable competitors to Sublime Text as Atom is; albeit the former two are only competitors on specific platforms.