If you asked me to improve Windows as a product for its customers, I'd probably be incapable of it. Not because there's nothing in Windows to improve, but because there's so many constraints placed upon it:

* You can't make it too powerful, integrated, or streamlined because you need Microsoft services to be artificially differentiated from competitors, which means leveraging platform power.

* You can't make it too fast because you can't overhaul any systems that might break a truly insane amount of backwards compatibility.

* You can't improve the UX because the primary function is monetization.

From a career perspective, head of Windows seems like not a great job.