I'll say it again; these rules are only for Class 3 arenas or lower. As you mentioned Dave, the rules limit the energy in the weapon and prevent shrapnel and debris from exiting the arena, as a Class 3 arena generally has a net/fabric roof and insufficient thicknesses of polycarb for full spinning weapons.

Both beetleweight arenas regularly used (Kinematic Events and David Weston's) are protected entirely by polycarb of an appropriate thickness, allowing beetleweight spinners to run without the restrictions required for Class 3 or lower arenas.