NCAP is not simply a concrete block. It has some sort of crumple zone on the block - and the frontal collision is offset to one side (as that is actually more common and presumably higher risk).
It is fairly logical that a higher mass vehicle will stand a better chance in a collision with a lower mass vehicle. However - since anyone using an NCAP rating in a purchasing decision is likely to be considering vehicles in a similar class it is irrelevant.
The Defender may not have crumple zones of it's own but it uses the other car as a giant crumple zone.
I have read of so many accidents where a Land Rover is in collision with a normal car - often the people in the LR have minor injuries whilst all the people in the other car are killed.
I saw an Army Land Rover go into the back of a Pug 306 at about 25mph. The Land Rover literally only had a dented bumper. If there had been anyone on the back seat of the Pug they would have been killed.
Now given that these "small" cars on the road have gone to fairly significant lengths to protect their occupants I find your "I own a defender so I
am safe" worrying. I realise you are a perfect driver and will never cause an accident. However I suspect no one kills someone else on the road (even if not their fault) and just shrugs their shoulders saying "they should have bought a better car".
NCAP is reviewed regularly in comparison to real crash data - and the general observation (e.g. google found this
) seems to be that higher NCAP rating = lower chance of fatality or serious injury.