As you noted, the locomotives are heavier, lower center of gravity and will track better with three axles per truck. Thus, they are less likely to derail when going through switches and curves.
However, the first car in the following train that had its manual brakes set would be a prime candidate to derail, dig in and take everything behind it off the track.
That is, the train would probably "break" at the first car which had its manual brakes locked. If there were any, that is.
If you look at the cars strewn in the LM rail yard ahead/beyond of the pile up it amounts to maybe eight - pretty close to the 11 hand braked claimed by the engineer.
I speculate that putting the hand brake on a car could be affected by the fact of having the main train air brake on. When the air brake leaks away, the forces in the brake pad generated by the hand brake setting could change (reduce).
Then there are the thermal effects (diurnal temps, letting the train's brakes cool after it is parked) on the various linkages and geometries (wheel diameter, brake levers, linkages, etc.).