The mid scoop is pretty considerable with both pickups set even on a Jazz Bass. It's probably the biggest reason that type of setup is preferred for slap style. I use both pickups set even for slap and for smoother finger style things. Otherwise I'm rolling a bit off one pickup or the other to add some presence to the sound. More front pickup gives more of a P-Bass (ish) sound and more bridge pickup is closer to a Ray (ish) sound, depending of course on where you pluck the strings. I can see the two pickup scoop could be beneficial in hard rock, for giving the guitars some room.
One of these days I might actually read what I've typed, before I hit the post button.