That isn't how I understood Dilbert. Dilbert is a normal guy and PHB is actually mentally retarded.
It's essentially gallows humor for a world where, for no apparent reason, blithering idiots often seem to be the only people who wield any decision making power.
Scott Adams had a take on that. The "Dilbert Principle" (his version of the Peter Principle) is that useless engineers that are promoted away from doing real work to keep them from messing it up.