I can't imagine why you would want elements in mix fight/competing for space It would just sound like a wall of mush, which is okay if it's some avant garde noise experiment, but not so much for a tight metal production or radio ready rock.
Listen to the best productions out there, and you'll hear there is insane amounts of separation between elements, but it's just done in a manner that makes it sound like it's simultaneously glued together.
And then go listen to Veil of Maya's "All Things Set Aside" album for hearing a really mushy sounding album where elements are just fighting/competing each other, at the extreme other end of the production spectrum.
I can guarantee the Veil of Maya sound is not the one you'd want.
I see no reason why not to use multiband on bass, some notes resonate a bit more with a particular instrument, no reason to cut it with a eq couse then you take that freq of other notes as well that might need it.