That’s not entirely surprising. Emacs’s UI is a character-cell matrix with some toolkit-provided fluff around it; VSCode’s is an arbitrary piece of graphics. One of these is harder than the other. (Not as harder as VSCode is slower, but still a hell of a lot.)

I use Emacs in textmode. It's super fast! But I've also never found VS Code slow, and that's with viewing multiple large log files at the same time