I play Allies usually, and i think the KT is fine. You should not expect M10 tanks weighing 3 times less, having an equivalent of cardboard armour alongside the KT, and with guns 12mm smaller to be able to easily take out a KT, i mean, why is it called KING Tiger. Also, the speed is fine, at about 70 tons, the King Tiger shouldn't be as fast as a the allied tanks.
The ultimate target to circle strafe much?