I have found Visual Studio Code to be more lightweight than Atom, resource-wise. Unless you are talking about lightweight in the sense of features?

Resource consumption is less of a concern to me than general 'snappiness'. Since I have a bunch of RAM, go ahead and use it all if I can have a good experience.

I don't actually use Atom, though I use Sublime full time. My biggest reason for not being able to use Visual Studio is that all functions, be it fuzzy search, regular text search, navigating tabs, even entering a character carries the load of the VSCode IDE. It must parse each character for chances to present additional information, which is great if that's what you want.

Subjectively, I find VSCode too laggy to work at my usual pace.

Atom is definitely NOT an improvement in that regard. Microsoft optimized the shit out of the parsing bits of VSCode, moving as much as they could into C++ Node extensions for speed and responsiveness. As Electron apps go, VSCode is tense nearly to the point of rupture. Atom has made great strides, but afaik is still not there yet.

VSCode does seem to fit that (increasingly less of a) niche for writing JS with IDE features, but it really feels out-of-place as a C++ IDE.

It's relatively good for Rust.

Yeah, I use Atom for JS and VSCode for Rust.