i honestly think that when RotJ was made, GL intended for force lightning to be a power exclusive to palpatine. just in the way that his power remained shrouded and in the end, and is unleashed solely in the form of lightning. as if he is so powerful with that darkside that he can use it in ways vader cannot.
then the PT comes out and GL gives out force lightning power to sith lords like its government cheese.
not interested in debating that, its just my take.