How do we make good design work when the deadline won't move?

You say the deadline is the problem. Look again. The deadline does not change its mind halfway through. What changes is your team's sense of what the work needs — it grows every day the work stays unfinished. This happens to every team that makes things under pressure. Craft wants more time. The calendar gives less. Left alone, constraints turn into excuses, and deadlines turn into shame. Neither one serves the person who will use what you build. Usually the real fight is not between craft and deadline. It is between team members who never agreed, out loud, what 'good enough' means. So people guess, argue, or quietly redo work at midnight out of private doubt. That is not discipline. That is disorder wearing the costume of care.