The tunnel design has not changed. And the tunnel is the main structural design of the chassis that controls its stiffness characteristics. The two flat parts for the electronics and the battery can basically be considered trays. The chassis is just as rigid from shock tower to shock tower as before. The XXX-s chassis is argueably the most rigid chassis in the TC market to this point.
In fact, the chassis is a definite improvement as it provides for better more secure electronics placement and mounting as well as keeping your battery more securely in the car upon crashes.