The point is that if Electron itself (i.e. using Javascript and the DOM) was the issue then both would suffer.
You might want to tweak the wording a bit - it reads like you're comparing Monaco to Electron, as if it were another app framework based on Chromium.
Since both VS Code and Atom use Electron as a base, so if the basic premise of using JavaScript + the DOM to render a code editor / IDE were flawed (i.e. it could never be performant), then both systems would be having issues.
This is what I was trying to state. If performance issues were fundamentally tied to the use of Electron, then you would see that manifest itself in both packages.
Oops, I thought you had written sdesol's comment [1]. Sorry.
The better analogy would be they are both built using Honda doors, but they each have completely different engines.