Quoth Myself.
I felt sadly inarticulate when I blurted that out in class at a loss for words, but I was hoping to make more than a subjective (unprovable) claim. I guess I was trying to tie hip-hop’s market viability to a claim that hip-hop is actually a complex, interesting, artful form of music that doesn’t rely on classical concepts like dynamic range to succeed as music. I think the best counterargument to the reading of “loudness” as decline is that the presence of loudness or absence of dynamic range does not equal musical simplicity, and the presence of dynamic range does not necessitate musical mastery. (Also related: musical mastery does not imply challenging or interesting music. See: The Ramones.)
So I guess Hip-Hop is a solid study on how loudness doesn’t defeat the challenge and complexity of music, and Hip Hop might be really good (question mark) because it has endured and really thrived among a wide fanbase ranging from popular radio fans to music critics.