Can we dispel this myth once and for all ?

New torsion bars and shocks are not required when adding a bumper.

Nissan puts the same torsion bars on a 4WD and a 2WD, and on V6 and I4 models, the difference between the weights can vary from 3500 to 4200 pounds.
Adding a bumper that weighs only 80 pounds more than stock will not make a difference.