I do have an idea about the Tomahawk buff. In standard tanking content, you're just using it for pulling or to take back some random mob you neglected that's torn off after a ranged character. For any sort of fights where mobs are dying willy-nilly(mostly I'm thinking PotD/HoH/FATE exp farming here), a lot of the time Tomahawk might be the only thing you can do to mobs before they croak due to distances between them.