How does a more rigid chassis improve my ride Comfort?

Do not confuse chassis rigidity with suspension stiffness.

The car’s chassis, or the skeleton of the car has to be stiffer in order to resist flex and twists for a more stable and smoother ride. The stiffer chassis will have a higher natural frequency thus making energy imparted to it by bumps less likely to excite the body’s structure. As such, a stiffer non-flexing chassis transfers more force on to the suspension where it can be dissipated by the Springs & Shocks instead of transferring the force to the occupants. Benefits are a Smoother, Tighter & Quieter ride.