IMHO, it was intended that Mace 'beat' Palpatine. Samuel L. Jackson was quoted numerous times that his only request to GL (other than the purple lightsaber) was that he "didn't want to go out like some punk" in Ep III, which means he defeats Palpatine only to have Anakin and Palps team up on him. I also believe that Palps' disfigurement was strictly from the lightning being deflected back. What I don't understand was his voice fluctuating, because he uses his ROTJ voice in all his transmissions and whatnot throughout the PT.