Yeah, OS runs faster only if properly written, definitely not using C# and fully platform independent approach. This applies for programs too.
And now we have problem - low cost developers and fast time to market.
Very good example how MS is not capable of producing decent SW are enormous bugs in literally every their product.
And its not only incompetent developers, also management who is forcing changes, eg Start Menu which is good example of generic (desktop, tablet) approach. That's bad!
But only way for things to change is to move away, eg Linux. But Linux is far away from Windows, but things change, eg Chromebooks.