I think it mostly illustrates how hard UX is to get right. There’s an explosion of combinatorial complexity in any non-trivial UI. The order in which users trigger events, how those event interact with one another, whether they use mouse or keyboard, their screen size, etc. It’s incredibly hard to account for all the different ways the users will end up interacting with the application. Also, I’d argue that you really want a UX designer on a team since it’s a different skill from software development. There is a reason we joke about developer UIs. :)