Still, culture operates on a "hubs and authorities" basis -- there are people whose job it is to be hubs (curators, publishers, music programmers and promoters) and people who become known for their genius ("authorities").
The interdisciplinary issue is interesting. There's probably enough of it happening to offset fragmentation of culture into specialisations.
My guess is that there are vastly more geniuses today but that they are spread out more geographically and to many more types of art.
Today, maybe Beethoven would be making techno in Rotterdam. Goethe might be making movies in Hollywood or computer games in Copenhagen. Who knows.