I'm not even talking about large files -- I'm only talking about normal interactions on small (1-10KB) files. Moving the cursor around in the text field, especially when my language plugin is in some mode that has some dialog up on the screen. Find and replace. Switching between open files. All of these operations often (but not always) demonstrate noticeable lag between keyboard input and screen output in VS Code (and Atom, of course).

Doesn't this look more like an un-optimized edge case than anything else?

Loading a 100MB text file is not really common, even among developers. Only logs and DB dumps are really that big.

I can't seem to open files of 1MB properly in Atom. Also I find it very useful to open logs to find-replace some info from logs.