You are missing that Chromium uses these APIs in the first place because they offer better performance or necessary flexibility. Since Google doesn't distribute Chrome on the Mac App store, chances are they don't care about "fixing" Chromium to not use them.
So, feel free to use Electron, just understand that your so easy to develop desktop app now hinges on the ability of a few unpaid developers (that's probably not you, or the "full-stack" people at Slack) to continuously keep track with the Chromium source and maintain their no doubt massive patches to its code to remove use of these private APIs.
So, feel free to use Electron, just understand that your so easy to develop desktop app now hinges on the ability of a few unpaid developers (that's probably not you, or the "full-stack" people at Slack) to continuously keep track with the Chromium source and maintain their no doubt massive patches to its code to remove use of these private APIs.