I think VSCode's impressiveness is less about the pure engineering challenge (although I do think even among popular, well-used IDEs there's a large differential in things like performance, which points to it not being a trivial problem), and more about making smart product decisions to strike a great balance between extensibility and performance / smoothness. There's not a singular big hairy problem to solve, but if you compare VSCode to other Electron apps, it's clear that the VSCode team really took the time to make sure everything was as performant and polished as possible.
And in terms of "well it depends on other technologies for it to work", this describes pretty much any innovation in software since the very earliest computers, including all the examples you listed.
Sure, we do all stand on the shoulders of giants. But the other things I listed requires significantly more research and development effort than building an IDE does.
Also I dispute that VS Code is the quickest editor out there. It’s faster than its Electron counterparts but that’s a pretty low bar. This isn’t a dig at VS Code, it’s my default IDE (well that and vim). But the largest part of the reason I use VSCode is because it’s free.
That, for me, is its real advantage. But that’s not an engineering achievement.
And in terms of "well it depends on other technologies for it to work", this describes pretty much any innovation in software since the very earliest computers, including all the examples you listed.