Did you actually give VSCode a try before making such statements? I use both (neo)vim and VSCode (with vim key bindings, sacrilege!) daily. Vim starts up faster (vim is instantly vs about 1 second for VSCode), but once you're in the editor it depends what you do in it. For instance the standard python syntax highlighter in vim is much slower in vim for files with a few hundred to a few thousand lines of code compared to VSCode. Setting up a C++ dev environment and debugger via vim plugins is hit and miss, in VSCode it's just a few seconds to install the extension, and step-debugging is snappier then in 'native tools' (e.g. Xcode).

TL;DR: it's not Electron or Javascript which makes editors slow, it's how the code is written.