One of the deficiencies of the city’s leading opera company, Washington National Opera, is that lately they think of Mozart as early opera. The last time the WNO staged an opera from before 1775 or so was Handel’s Julius Caesar in 2000 and the same composer’s Agrippina in 1992 before that. Baroque opera is one of my major interests, and Handel is great, but there is a century of Baroque opera before Handel, too. We…