Only back then it was true. Now it’s only slow on Windows for some reason (and maybe not universally so, though I don’t use Windows enough to have bothered investigating).
While that's true, what's not slow on windows except maybe AAA video game titles? e.g. the "right click" on the Windows 10 desktop takes time to show up (even on a high end desktop pc)... just to show a contextual menu.
It's still very slow with a lot of Elisp code (Spacemacs, for instance). Maybe the memory footprint is better than VSCode, but VSCode starts faster and is more responsive than Emacs with a ton of packages.