I'm an economics major, fully familiar with the use of the term deadweight loss, and what you're arguing against is welfare economics 101. All forms of tax, subsidy and quota including licensing shift supply and/or demand curves to new equilibria which are different from the unregulated market equilibrium; the purpose of the Pigouvian tax example was that the unregulated market equilibrium is not necessarily the "correct" reference point for calculating deadweight loss in the presence of externalities and information asymmetries. Similarly, comparing wages between licensed and unlicensed professionals across different licensing regimes is useful as a method for estimating deadweight loss from the licensing regime only in the event that there is no benefit from the licensing (i.e. it assumes no externalities related to licensing exist and licensed and unlicensed professionals are undifferentiated in average quality and in an efficient market ought to earn the same amount)