To me this more proves quite how poor HSTs and Mark 3s are in comparison to modern stock. The 390 involved at Greyrigg came off the line at 95mph, went down an embankment, tumbled and remained structurally sound, mostly intact and coupled. As I understand it linespeed here was 75 but its likely the HST was doing significantly less, and we have one coach demolished, two upside down, one on it own down an embankment and a severely damaged power car.
I don't think one can really say one way or other on this. It *looks* to be the case here that the train has jack-knifed and then one of the carriages ended up getting wedged in place. No vehicle is going to come out well in that situation, the energy simply has to go somewhere. Had the remaining vehicles collided end-on then something like a Pendolino might have scored slightly with the crumple zones collapsing in a controlled way, but in this case the damage looks to have occurred mainly as a result of the vehicle having been crushed and having no escape route.
As regards a 158, the circumstances would have been completely different had it been a 2-car unit as there would have been less vehicles involved, and in this case most of the damage seems to have arisen from secondary collisions. So the fewer vehicles involved the better. But equally there would have been passengers in the leading vehicle who would have needed protecting from impacts with external objects like trees.
Quite simply every accident scenario will be different, and tiny things can have a big result on the outcome. I seem to remember that the outcome of Southall was heavily influenced by something small falling off one of the trains which then deflected one of the vehicles in a particular direction.
It is *way* more complex than just saying one type of train is safer than another. Ultimately in a collision there's a massive amount of energy to dissipate, and it has to go somewhere.
Having said all that, the structural failure of the HST power car's cab is cause for some thought.