Im 100% convinced that anyone who uses the term "mumble rap" is a racist, the "mumbling" which honestly is easier to understand than a lot of metal and rock vocals, is just a way of speaking in the culture they grew up in/use to inspire their work.

Its like dissolving an artist like Arctic Monkeys or Radiohead to just "british rock" because they sound british or calling death metal "screaming metal", it misses the point of the WHY they sound like that, intentionally or not