As a qualified flying instructor I have been thinking about this accident. Until the final report is published we can only speculate as to the probable cause.
Error chains can start a long way from the final event. If during flying training a loading calculation and performance calculation was made for every single sortie would this go a long way to eliminate performance related accidents? In the airline world it is taken for granted that a correctly appended loadsheet must be produced and signed for, also that Performance is checked for every takeoff. The latter is often presented in a "simplified" form to enable rapid and accurate calculation.