Emacs modes normally use regular expressions for everything from syntax highlighting to semantic insights. This does not make it fast. Emacs performance usually degrades linearly with the size of the file being edited, and most CPU activity occurs synchronously and blocks the UI.

I don't think Emacs is a fast editor unless you run it bare with -Q, at which point you've left out all the stuff that makes Emacs useful.

IMO it ought to provide a state machine engine for modes to use to do syntax highlighting, something that it can cache at line boundaries, stop and start electively depending on bit of the buffer is displayed in the current window, evaluate the state machine on a background thread (so, concurrent with actual usage, unlike the idle work it already does), etc. A state machine without extra knobs would only provide lexical highlighting, but I think extra knobs (e.g. variables, stacks) could be added to make it more useful.

The retained mode text styling with font locking etc. is not the optimal design choice for performance, I suspect.

Emacs, at least in windows, can be surprisingly slow. I think they have fixed some issues with long lines, but those used to be aweful. Also large files can be slow. Also, too many packages is a problem, which we might well see in the future for VS code, too, but the javascript runtime is likely orders of magnitude faster than the emacs one, no?

vim, on the other hand, is supposed to be really quick as far as I have heard!

I only use Emacs on UNIX systems and it is quite fast.

On the old days I was usign XEmacs, which did not had any issue with Windows.

Now if someone is running Emacs as cygwin application, then it might be slow I guess, given that everything on cygwin is slower than pure Win32 applications.