Slack is a messy one page app developed by PHP programmers and vscode is open source and actually made by competent people.
What I don't get is why they don't want to make a native macOS client, or Windows client. For Linux I get that they don't necessarily know if it should be GTK, QT, should they adopt KDE standards or Gnome, something else maybe? I can see why they would like Electron in that case.
For something like the Mac... They could do a fantastic client, it would use very little memory, play nice with the OS and be fast. Their users would notice and love it.
Doesn't it kinda make you think, just a little?
The hubris is frightening.