My suggestion that Scarpia occupies a more focal position than Tosca in Giacomo Puccini's opera based on Victorien Sardou's drama named after the latter heroine may have had its origins in my student days when I first started reading arts criticism. I remember an issue of The New Yorker in which Winthrop Sargeant described Frederick Ashton's choreography for the ballet Cinderella as the story of two very droll old maids who happened to have a beautiful stepsister who went to a ball and married a prince. (Mind you, those old maids were originally danced by Ashton himself and Robert Helpmann, both of whom were comedic experts as well as superb dancers. It is easy to imagine them upstaging even the likes of Margot Fonteyn.) These thoughts on finding the right focus were further cultivated by Joshua Kosman's account of the new San Francisco Opera production of Giuseppe Verdi's La Traviata in the San Francisco Chronicle:
From its second act onward, the San Francisco Opera's new production of "La Traviata" attempts something radically new with Verdi's familiar melodrama.
In this version, which opened Saturday night at the War Memorial Opera House, a well-meaning but short-sighted father, Giorgio Germont, comes to grief when he attempts to stage-manage his family's affairs in accordance with bourgeois morality. It's a darkly moving tale, with hints of a Sophoclean downfall.
There are also a couple of younger folks in the story - the hero's feckless son and his tubercular girlfriend - but it's not always easy to get as worked up about their problems.
Unfortunately, those young lovers - Violetta Valéry, the "fallen woman" of the title, and her devoted Alfredo - are actually the focus of the opera that Verdi composed. And Saturday's dramatic realignment was the result of some deeply disappointing performances that allowed baritone Dwayne Croft as Germont - recovering from a sinus infection, no less - to walk off with the show.
I suppose it comes down to whether you want to choose your focus on the basis of "star booking" (which is basically the reasoning behind that last paragraph) or a well-founded narratological argument (which is the strategy I tried to take in writing about Tosca). Germont may not spend as much time in a spotlight as Violetta or Alfredo; but we can make a good case for him being the primary source of motives for the entire opera, not only those of his own "bourgeois morality" but also those of the would-be "lead characters." I am not sure that I would call Germont a "Sophoclean" character; but, under only slightly different social circumstances, one could seem him as the subject of one of Euripides' plays.
The fact that one can choose one's focus stems from Gérard Genette's approach to "narrative reality," which distinguishes between the plotline (or "story") as a basic time-ordered sequence of events and the "discourse" strategies through which those events are presented to the audience (not necessarily in temporal order). In other words, the "story" (in Genette's technical use of that term) is not about anything (since it consists of nothing more than its component events); the significance of the story only emerges through how it is told (hence the old joke about a child's report on a book about Lizzie Borden, describing it as the story of a girl who was not very kind to her parents).
In all fairness, however, I should observe that, while I could come up with evidence that, regardless of how Sardou may have conceived his discourse, Puccini's Tosca is very much about Scarpia, I cannot make a similar case that Verdi thought of La Traviata as being about Germont. If Scarpia is with us from the very first note of Tosca, then the dying Violetta is there in the first phrase of La Traviata, which we shall then encounter as the prelude to the final act in which that death is depicted. (When Franco Zeffirelli conceived of this opera as a film, he took a similar "flashback" approach, having the camera walk through Violetta's rooms after her death while the orchestra plays the opening prelude.) It is hard to imagine Verdi as ever wanting to write an opera about a character like Germont; but, in today's world that has become so fixated on "family values," it would not surprise me to find an opera composer willing to take on the task of giving this epitome of bourgeois thinking his due.