Because the first Bane lacked controlled movement (before the invention of Melty Brain AI), Urjak designed the second Bane to be a SnS that was fully controllable. This Bane was not as good as its predecessor.
Despite Bane III's potency, its shell panels were left exposed by the razor placement. After placing half the razors on the top and half on the bottom, Bane IV's design became an archetypal LW Flail Shell Spinner design.