This seems to be the main source: https://twitter.com/TheLarkInn/status/1006746626617008128

I thought they published an article that explicitly mentions RN but I can't find it at the moment. MS has also been heavily working on RN for Windows including a C++ bridge that significantly increases the performance of the JS to native bridge.

That's really insane, although it makes more sense than, say, writing a code editor in Javascript.

Does it? VSCode is refreshingly quick while Word is (already) brutally slow.

Just switch Word to draft (nee Normal) render mode. It was never meant to be performant in print layout mode.

But that’s how everybody uses it. That’s the default mode when you start a new document. Who even knows that the other mode exists?

Surely they could make it performant in the default mode that everybody uses now that it’s 2019 and we have megahertz to spare? There is no excuse for Word’s atrocious performance.

Draft/normal was the default in Word 2003. Most people have used it.

The problem with page layout mode is that any non-trivial format change, insertion, or deletion requires repagination and the UI freezes until that is completed. Draft mode repaginates asynchronously so that it remains responsive. Comparing a WYSIWYG editor to a plain text editor is no contest as the former performs much more work to layout the text.

I use Word a lot on documents of varying complexity and size range from one to about 500 pages and, other than doing something like a TOC update on a giant and complex document, I've never seen Word be painfully slow, even in Print layout.

Painfully (and randomly shifting) inaccurate in print layout on documents that involve more than just text, sure, I see that every day.