I've said this before on MalwareTips. If OS can't run anything useful it won't be vulnerable. But then, what are you going to use it for then? Windows is so vulnerable because it's so widely used and because it's so configurable and adaptable. As soon as you take that from it, sure, it'll become way safer. But then you won't be able to change 3/4 of things you can now. There is no middle way as you'll always sacrifice something, be it customization or security.