Dave, you are right but that is the problem. Its certificated.
All:
1. Watch this 777 evac certification test.
2. Count the number of pax with hand baggage.
3. Reflect on the holiday destinations that this high density configuration is designed to serve from EGKK.
4. Think about the type of people that will use economy class and how often they travel in an aircraft on average (most once or twice a year), and the fact that they tend to take max hand baggage.
Pinkman