Should be nerfed by 90%.
50% still makes it better than other equipment.
It was the same with the Void Stone trinket, nerfed by 50% but still too good.
Not 100% sure about Prism as in truth I have not done any research after its nerf, but I am 99% confident that Void Stone could potentially be a BiS PvP trinket even for non-Intellect users.