Is the assumption here (flipping over = very bad) correct? Is it possible that [edit: the force] can dissipate more easily if it flips (provided the car is built correctly to withstand the force of a flip)?
NB: I know nothing about this topic, genuinely curious to hear from someone who does.
I think you're on to something. The people in the small car were almost certainly harmed a lot more than those in the SUV. Just look at how hard it slams into the SUV. Provided the seat belts are able to hold the passengers in the SUV in place, I think they survived without much harm. I'm more worried about the passengers in the small car.
I'm genuinely curious about this too. In my uninformed opinion, for a car that's heading toward an obstacle (e.g. car, truck, pillar, wall, lamp post) there are a few possibilities:
1) heading straight while braking: probably the best case as you have the collapsible trunk between you and the obstacle, and you can reduce the speed, if by little;
2) spinning without control and crashing with the back or the sides: worse than 1), but not so bad as there are side airbags and the headrest. The car is at least somewhat protected on all sides, plus there's some tire friction for reducing the speed;
3) rolling over: less friction as the car is rolling, plus the car may crash into the obstacle with the car's roof or floor. Both are certainly more than a layer of tin, but not as protected. Plus, objects flying around the car and limbs in an unsafe position when the crash happens.
Modern cars are incredibly goo at absorbing shock from the front and rear directions. They are much worse on any other direction, wether it is lateral or vertical. The flipping means everybody in the car had a huge shock the first time it felt, probably worse than anything people suffered on the other car.
Flipping also does not help stopping faster (in case there's something dangerous ahead). Instead, the faster way to break is by using the wheels just like the car is designed to do.
NB: I know nothing about this topic, genuinely curious to hear from someone who does.