I've heard it, and I've said it. I've been in a number of projects where we had engineers sitting around without enough work to do, because user stories were not in "ready to work" state, pending UI/UX stuff. Eventually - because it isn't like anyone can wave a wand and either make the UI/UX folks work faster, or magically get more folks hired - the developers and project managers just plow ahead with minimal UI/UX work.

J.Ja