With all due respect, that's rubbish. Modern airframe designs tend to make greater use of lightweight materials and technology, but with advances in CAD and engineering tools load calculations can be simulated far more accurately than was once the case, meaning that the need for overengineering is reduced.
Calculations and simulations are not done for a variety of crash szenarios. It is the overengineering which produces the margins for unplanned loading of the airframes.
I agree that the 737 is not the best example of a robust airframe... But there have always been crashes where most passengers walked away because the aiframe stood strong. Some Fokker 100 (Austrian, Air France), MD11 (Mandarin), DC-10 (Iberia, Garuda) come to mind.
Nevertheless, the 777 fuselage indeed demonstrated excellent structural crashworthiness behavior.
