^Fair enough and true statement. The chassis and receiver do see all of the reaction from the tongue weight and lateral and longitudinal forces. However the wdh eases the load on the rear axle, suspension and wheels, which are typically the limiting factors for towing compared to the "frame" and hitch.
With the SRat Durango having a solid rear axle and quite literally a drivetrain and brakes that are either on par or better than a 3/4ton truck, combined with low CoG, stiff handling and about the best technology available for stability control it is actually overkill for towing "only" 8700lbs.
If in sport or track mode, that's like tow haul or super tow haul mode and stopping is aided by a transmission that will rip off high rpm, locked tq converter downshifts as fast as the 6 piston brembos can clamp down on drilled and slotted rotors that are bigger than the rotors on my diesel cummins, with brake pads designed for track use. Again better "equipment" than most HD trucks.
IIMO the only "weak" points if you can call them that is the active suspension damping that will get a hard workout in the rear and coils that are guaranteed softer than a 1/2 ton truck (a little).