While i totally agree with the approach you suggest towards making UX Design Route choices, the priority of usability design shouldn't be as high as core-archit

While i totally agree with the approach you suggest towards making UX Design Route choices, the priority of usability design shouldn't be as high as core-architectural design, simply because driving you're application from usability towards functionality can never be a sustainable solution to the design of any product. For instance, no operating system can ever be designed with its user interaction in mind. While it does have a critical impact in OS design, there are far more critical issues that UI has no say over! That being said, it largely depends upon the impact of Usability on your product's overall outcome. Correct me if i'm wrong!