Stability control still more important
Statistically, the number of rollover crashes is pretty low and becomes even less likely with stability control. People don't die because of weak roofs. They die because they're not wearing seatbelts. Also, IIHS and NHTSA can't agree on a standard. IIHS wants roof to support 4 times its weight while NHTSA seeks 2.5 times. Either way, seat belts and stability control are more important.