[For palm muted powerchords and fast riffing, the JB wouldn't be my first choice.
If your bass player has a tight, punchy, tone that dominates the bass frequencies, the JB does a fine job of filling in the mids and low mids. It is loose on the lows and it kind of roars, but it does fill up a lot of space.]
Well, for metal PM riffing at least Dave Mustaine must think it is okay..
Of course it's a matter of personal preferences, but it isn't strictly bad for metal/rock rhythm playingm it's just not the best choice to go with bright amp and guitar.