IMHO, critiques of "vulgar" I believe -are- personal in taste. Because one person's "vulgar" is another person's "pristine", I would extend this question further. To what end does a dancer display their "rough edges" of their personal life onstage as a performer? Those of us posting on this site who are ex-dancers, staff and or behind-the-scenes stakeholders in ballet know all too well how much an illusion of perfection as little girl's view of her first Nutcracker. How many dancers you know don't glide off stage, pull their bloody feet out of their shoes, pop open a beer and snatch a smoke? There are many. And crudity is also "common" in the off-stage life of many of us. In fact, it virtually comes with the territory. There are relatively few dancers who are as pure in reality as the fantasies and fairy tales they portray on stage.
"Common" could be an interesting term to use for Somova. Obviously, the speaker was referring to an overt display that betrays the intention of the artist to create art versus the intention to "wow" or display ability. Somova's extensions are -not- common in the literal context, but may be "socially common", due to the relatifvely young Somova's seeming desire to show off her unusual rather uncommon talents. Maybe such displays should be left to Cirq du Soliel's contortionists, versus "La Bayadere. So, rhetorically asked, does a dancer's ability or talent often get in the way of their ability to communicate artistry? Does their maturity and age?
I think it true that traditional antagonists like Madge, Coppelius, and Carabos may actually be staged and/or interpreted to be vulgar. Without the vulgarities, the character may not help drive the plot in a specific staging or production. However, there are those stagings and performances that are -not- overtly vulgar of the same roles. For example, The late John Goding's performances (Washington Ballet) of Coppelius lacked the crotchety quality most (including my own) interpretations use to carry off the role. His had almost an undertone of elegance. Instead of a mad curmudgeon quasi-Einsteinian tinkerer, his was more of a studious inventor working out his issues of self-imposed reclusive loneliness with a doll. (ehem...please don't carry this further into most our artistic imaginations than I intended it too,
So, I think most often, their vulgarities are a choice first of the performer and choreographer/regiseurre/ballet master's staging. Its no news to most of us that use or belief in such determinations as vulgar and "common" are a personal reference to taste and beliefs based upon one's own experiences. Indeed, (as stated) Kevin McKenzie's Rothbart could be viewed as "vulgar", but is he not intended to be so? In this, cannot such a performance of a vulgar character be brilliant? IMHO, Marcelo Gomez' performance is breath-taking, to me, the best part of the production. But, maybe folks prefer the traditional acting dominant version of the antagonist, hmm.
In short, I think vulgar vs. elegant or decent, common versus rare or coarse are adjectives left to those of us with opinions based on experience - (which means just about everyone in a free society, LOL!) For example, I think there is likely a strong contingent who agree that Tom Delay was just as vulgar a politician as his is attempting to be a "dancer".
For me, I find the competition scene worse than vulgar; I believe it to be corrupt and unethical. But, this is another discussion.