I respectfully disagree with that first statement, because I feel it may contradict the second. Be the bass player and lock in. That is your duty to bass and your duty to the audience!
Perhaps add some flare once in a while, but keep it to a minimum. There's a way to play less and say more.
Disclaimer - I'm a jazz bassist before anything else and my opinion may not exactly match up to your style. Take it or leave it, just play strong.
When you said jazz that explained it. It would seem very contradictory in that sense but in metal the guitar and kick drum can hold it down. Not to mention the guitar is pretty heavy with the distortion. I do prefer to have my bass on the rhythm more now though and I'm given free range to do lead ish parts
