I don't understand why it's freeing up a slot on your DRK? Do you have Shield Oath and Sword Oath accessible when you play DRK? With my weapon drawn, I have access to 2 crossbars and an extended crossbar which displays only skills for whatever job I'm on. If I switch jobs then all the skills on those crossbars change accordingly.

When I sheath my weapon I have access to open world buttons, like teleport, mounts and gearsets.