Well, MS Word 5.1a on a mac ran really fine, as did all the Apple/ClarisWorks software. Word Perfect on a PC ran fine, too. Then came the inevitable bloat. Later versions of MS Word didn't run that smooth anymore, ClarisWorks became unsufferable. WP killed itself.

There's still lean software. Mellel (for macOS, https://www.mellel.com) is a very responsive editor, with a style edit model that's a bit different from Word. But it takes a lot of work to make something increasingly capable and keep performance.