If I were writing the prequels, I would have had Episode II end with Anakin being dubbed "Vader". From his perspective in Universe, it wouldn't be an evil or strange thing at all, nor would he even be aware of the lore of the Sith. It'd be played almost like a secret promotion from the Supreme Chancellor. He'd still remain in the Jedi order, he wouldn't turn on the Jedi or say they're evil, but we would have seen him give in to the dark side seeking selfish power for himself. He would have been secretly a Sith throughout all of Episode III, trying to split his allegiances until the very last moment, but all of the events would play out the same in that movie.