Vader sans sith lightening ...
Dooku / Darth Tyrannus uses dark force lightening on Anakin in Ep.2 ... and he's supposed to be a fallen jedi ... who studied the ways of the dark side for 10 years.
Darth Vader was a master sith lord ... and a sith lord in no way inferior to Darth Tyrannus / Dooku as a sith lord; so if Dooku had the power to wield sith lightening then theoretically Vader should also have had the power to strike with sith lightening. Now obviously the saga hasn't progressed in order from ep1 to ep6 ...
and at the time of ROTJ, Lucas gave the sith lightening power to the emperor, I suppose, to make him special in some way as befits the supreme sith master. At that time, he didn't know that 16-18 years later he would be filming episodes 1 - 3. And that he would come up with this thing of the sith always being 2; master and apprentice; no more no less. And that in episode 2 an APPRENTICE sith ( i grant u that Dooku is not exactly an apprentice but a fully fledged force master himself, but technically he's still the apprentice to palpatine's master ), would be shown wielding the sith lightening. The thing is, it's a simple equation; anything that Dooku can do with the darkside of the force, Vader can do as well; i.e. if Dooku has the power to strike with sith lightening, than Vader should also have the same power, because he was in no way inferior to Dooku as a sith lord.
But obviously Vader never had the sith lightening power ...
therein lies the anomaly .....