But maybe the genius didn't kill dramaturgy. Maybe it was more like that time in Sleeping Beauty, when the prick was not death but simply a long snooze. Sometime around the late nineteenth century, dramaturgy's concerns with reason were re-awakened: the kiss came not from a prince, but celebrity playwright and mutton-chops George Bernard Shaw.
Before he became a playwright, GBS was a critic. It's frankly difficult to tell whether he liked a play or not from his reviews, but it is clear that he liked himself quite a bit. He's got a touch of the Lessings about him: the subject composedly under considerable is just a platform for a long leap into whatever had GBS' attention.
Between mocking Shakespeare, GBS championed Ibsen. He liked the naturalism. When he got around to writing his own plays, GBS majored on 'the play of ideas'. A ghostly Diderot would have given his thumbs up, although he might have found the speeches a bit ponderous. Never mind: reason and political engagement were back on the menu.
But, of course, it's Brecht who really revives dramaturgy. He used dramaturges in his Berlin company (although they did everything from get Bertie's suits from the cleaners to writing the damn plays), and even wrote about a new kind of theatre - the epic - that challenged tragedy on the grounds that it presents events as inevitable. His alternative, which led to things like forum theatre, regarded the theatre not only as a locus for public discussion but as the place where change could happen. Sometimes, like at the end of The Beggar's Opera, he'd even point out why the play was not like real life.
Whether or not anyone was actually reading Diderot - and in the UK, the answer was probably no, as he has never been taken that seriously in theatre studies until I came along - dramaturgy in its full rationalist, engaged and revolutionary glory. And it didn't hurt that GBS and Brecht are thought of as geniuses (if we still think about the mutton-chops at all, that is...).
The chat about dramaturgy these days comes mostly from this revival. Brecht is so influential that you'd think he invented audience participation (actually, pantomimes did that about half a century earlier) and his 'alienation effect' (reminding the audience that they weren't watching reality but a play, usually by having a stage-hand wander across the stage every so often) gave permission to subsequent generations not to worry about scenography too much.