Stu, you ask many questions, as if dancing back and forth on fallen trees—vectors?—crisscrossing creeks. Dead or alive? IX or UX? IX or IA? Mature or infantile? Its own job or being 'jobbed' by others? Many of these are just victims of attempting to reduce any debate to a single word. I've learned the folly of that from our politics lately: whenever you attempt to reduce something to a single word (name-calling, such as 'activist judge'), you are simply finding a way to disagree with one another. UI design—I'll stick to my name-calling of preference, tracing my first credential in the field to the pre-pubescent year 1985 (a magazine review comment on the user-friendliness of my work)—has many maturities and immaturities. It is part of many jobs and often quite apart. It is the tasks that a coder or PM often will not do well or cannot do at all. It is, as you bottom-out on, 'design.' Look it up, there's essentially no definition of the word, just describers. On the flip side, identifying a matter with a single word—name-calling—whether trying to nail down a mundane job description or a lofty practitioner's philosophy (design thinking), is a dance step to learn.