At least on those 4-across planes, there is an escape hatch for high $ travelers: The F cabin. If you are GS or even likely 1K on a D+ fare, you have a very good chance of being able to upgrade yourself to the best seat in the UA fleet today. Or, your plane is swapped to Polaris config. Win-win.
Certainly that isn’t the case for most, but it is one reason UA keeps its high value folks happy.