> Wouldn't it be better to make native application

Actually there are such editors. I use vim instead of vscode or atom. And I think my installation of vim is slower then vscode because of some plugin that I've not found yet.

Applications like vscode very useful because they help to find performance and other bugs in browsers. Same way as browser improved when gmail and sites like this appeared.

I would support appearance of IDEs, large games, VR, image and video editors in browsers as they help improve web platform.

If you don't like it, just use other option. It could be faster, but may be not. Not sure that vscode is slower then visual studio for most tasks.