A sustained increasing load is tougher on the car than an “explosive” load. The video you posted of the Volvo rollover, the roof doesn’t even sustain anywhere near the forces the IIHS test exerts on it as evidenced by the Volvos deformation under that test:
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In the Volvo rollover video the roof is sustaining forces yes, but the car is rotating as it hits the ground so it’s not a sustained force on the roof, it’s glancing hits. In fact the wheels and sides of the car take a lot of the impact. Additionally you realize a majority of the roof is just thin sheet metal right? The IIHS test is equivalent to dropping the car from heigh onto its roof rails. It’s not a perfect test, but it’s a good representation. With the pano sunroof the Volvo also doesn’t have any crossmember support and just a beam at the windshield and one towards the rear:
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And if you think Tesla is gaming their rollover tests go watch some moose tests. The Model Y had no issues. Part of rollover safety is not having a rollover in the first place: