I think this is a good point. Now, of course, there are issues with using that descriptor as well as there is a healthy debate whether the avant-garde even exists anymore. As @parrishcouncil council observes, the avant-garde’s ‘shock of the new’–to borrow a phrase from Mark Fisher–was definitely a distinctly modernist characteristic. Though I’ve never really liked that vague notion of ‘newness’ that Reynolds and Fisher so often invoke…personally I think “fringe” or “on-the-margins” is more descriptive while also remaining open and flexible.
Genres have always served a distinctively linguistic purpose and often evoke either a quality, attitude, or geographical origin of the music that allows listeners to talk about a wide range of artists under the same umbrella. I think everyone is expressing a similar frustration in that we are lacking a critical language that is growing and responding with today’s musical developments, which are also more nuanced and less obviously ‘new’ than, say, jungle’s mutation from hardcore.
And this is a more general observation, but I’ve noticed that American dance music fans tend to put much less of an emphasis on genre than Europeans I’ve met…though both groups seem to ultimately find either approach lacking as the endless proliferation of genre names makes the music arguably more inaccessible or intimidating to a newbie. I realize I’m just pointing to the existing questions here, and that’s because I’ve been trying to work through this issue myself. I read a GREAT essay from 99 on genre mutation within electronic music that identifies some really illuminating structural dynamics. Its reading of the neo-industrial impulse is eerily prescient.
Monroe, Alexei. ‘Thinking About Mutation: Genres in 1990s Electronica.’ Living Through Pop. Ed. Andrew Blake. London: Routledge, 1999. 146–158.
And reading this currently…not sure if I love it, but it definitely helps fill in some blanks on avant-garde theory.