xhonzi said:

Maybe I need to give up my vision of full on Jedi vs Dark Jedi battle.

The way I see it, Vader is special. He betrayed and murdered the Jedi. If he's one of a giant army of Dark Jedi, he beceomes significantly less special.

I also don't see in the OT any sense that the struggle of the past was bad Jedi vs good Jedi. The Jedi were guardians of peace until the dark times... until the Empire, not "until a bunch of Jedi either turned bad, or another competing force of bad Jedi had war with us."