I'd agree on vim being of limited utility when it comes to automated refactoring (it's a text editor after all), but beyond changing the names or extracting functions what can an IDE do for you in this respect?
I've tried the ctags-indexes with Sublime and afair the basic navigation was not bad (I think I remember there being an issue with some delay though? It was a while ago). I'm not sure if things like "show code which access this variable" or "show all children of this class" are supported though?
Apart from those advantanges, I can think of two more:
1. IDE can import your build file (maven, sbt or bazel project for example), parse out the project structure from it and download the necessary dependencies. I don't think that ctags-like powered solution is as robust, which means you'd have to fiddle with it until it can understand the structure a complex repo.
2. IDE can run and show the results of unit tests. (just right-click on test you want and select "Run" from context menu).
it takes about 15 minutes for Visual Studio (well, visual assist) to generate the index for the project, and then the navigation is instant. I've tried a few times over the last few years with various language server and clients, and my experience has been the same pretty much every time.
You lost me here.
> I don't see how "UNIX as an IDE" delivers this.
Have you read the linked series of articles? The author explains and provide examples with C and Perl, Iirc there's a book about working with Makefiles in Java, so it's totally doable, painful, but doable.