honestly? i think that loosing half your beast gauge upon switching is one of the major balancing factors with warrior. its designed so that you have to dump all your gauge before switching so you actually need to know the fight instead of being "ooops i need to be in tank stance now, let me just use my oGCD swap". This being said however, i do think that when you swap it should take half away BUT round it up or down to the closest multiple of ten.
