I agree that we should focus on designing what to build, I struggle with this question everyday working in a corporate setting. At the end of the day, it's all about revenue and that dictates what is to be built and when to pivot. Designers can create a pain-free, intuitive experience for users but when you have product management defining requirements and use cases, your hands are tied in respect to "what to build". That simply isn't seen as our job unless it's your company or you are a UX researcher tasked with uncovering unmet market opportunities through user (segment) research.