Is it me or is the bass guitar treated as the red headed step child in heavy music? Unless I'm listening through a quality sound system, I have a hard time picking out the bass guitar. It might just be the result of a lousy final production, or it's just so distorted it comes across as a third guitar, but when I can actually hear it I find the extra dimension it adds to be very worthwhile.
Listen to a song, cut out the bass and you will hear the difference.
It is not necessary to use huge amounts of distortion to sound brutal. Paul D'Amour (formerly with Tool) did not have to use a distorted tone but instead played aggressively on a down-tuned bass with a strongly picked sound.
Bass guitar in "heavy music" is quite key to contributing to a "bigger", "chunkier" sound...but guitar players can also hang a little around in that domain using low tunings like drop D - or, even drop C.
Daron Malakian of System of a Down even used baritone guitars live and on some records.