That said, large companies using Electron is what I don't get. You can't expect me to believe Slack doesn't have the resources to create an actual app for their product.
Also they might have started in electron and now it's hard to move away from it.
You can relate if you ever had to setup a JS taskrunner/webpack from scratch. If you don't do it regularly, expect to spend 2-3 hours going through documentation and lots of outdated StackOverflow posts.
JS is easy as long as you stay within the constraints of whatever scaffolding you're using, if you need anything outside of that or need to upgrade your stack you need to know a lot of little things. "Best practices" move fast in JS, and projects die fast too.
Our companies customized eclipse on the other hand hogs 8GB ram when doing nothing, needs 2 minutes to start, and is sluggish in general. It's our course written in Java, which is much closer to native than electron, but still they wasted resources everywhere they could.
You can't run a compile on a 8GB ram machine, it will start swapping to hard disk.
Sublime doesn't have all the features, notepad ++ neither, and I just don't like vim style editing.
That leaves vscode.
So it's not Electron, but it's what Electron enables.