The safest seats are those with firm cushioning that holds the occupants in place. This provides the least space for acceleration in a collision. They are also the most comfortable for long trips, affording support which prevents fatigue.
There is no excuse for GM to not have a good chassis to start with on the 5 cars they base off of it. Maybe if the Epsilon chassis was decent it would be able to sell at MSRP. Even in its sportiest iteration, the Saab 9-3, it fails to feel very sorted out. It’s just not a very good chassis, and no amount of firming the suspension, widening the tires, deepening the exhaust note, or giving the steering a heavier feel can mask it.