That’s...uh, surprising as hell. The idea of a designer that could actually tolerate having to use Windows full-time for design work, even at Microsoft; would be much more surprising, from my experience.
The lead designers at Ford might drive Porches on the weekends, but I'll bet they still drive Fords into the office.
The more painful it is to eat your own dogfood, the more it's necessary to do so. But it has to be mandated from the top down.
If the only people with the power to actually change the product aren't even using it, the god-awful UI/UX decisions in the latest version of Windows begin to make sense.