I use an IDE written in non-native code (IntelliJ) and I can have dozens of files open, while the IDE does error checking in the background across thousands of files, and it uses around 2GB of memory in that situation. 800MB for one file is insane.

This isn't just a contest between native and non-native code. It's a contest between efficient non-native code and crap non-native code.

Xcode is about as native as you can get (developed by the same company as the OS!), yet it becomes more sluggish with each new version. I think the real problem is product managers focusing too heavily on "shiny new features" and less on efficiency/stability, which is mystifying since these are all dev tools, after all.