I can't see why a bluegrass songwriter wouldn't benefit from learning more about rap, funk, metal; bringing a stronger context to their understanding of their own genre (which is sometimes an arbitrary delineation) and perhaps some techniques.

> It's not that a successful country music songwriter can't listen to and enjoy hip-hop but you'll find they tend mainly to listen to and be influenced by country music.

Without any examples for or to the contrary, I'm not convinced this is true.

> The point of the article was in encouraging writers to hone in on an individual voice as opposed to being influenced by thousands of competing tones.

I think both extremes are harmful. But my experience comes from dabbling in Jazz music of all sorts; 'Jazz fusion' is such a broad moniker that it extends from funk to rock to swing to rap.