I came the other way very recently (emacs to VSCode). It wasn't performance that was the issue, it was the level of effort required to get the same level of experience between VSCode and Emacs.

I have used Emacs for about 10 years, and have days upon days of effort invested in my emacs config. Despite this, it took 5 minutes of setup to get a significantly superior setup for the languages I'm using currently (Elixir, Rust, ReasonML, Python). I had more features available (e.g. better highlighting and listing of current errors), and the core ones like auto-complete and go-to-definition worked much more reliably. It took an hour of tweaking some keybindings and settings to remove some UI cruft and navigate between splits and I have something that performs at least as well as Emacs in every regard. It's only been a couple of weeks, but it's promising so far.