If I may, one thing you have to consider that is, due to Bane's Rule of Two, the Sith would only exist as a Master, and an Apprentice, for power reasons. It was to maximize the Force between the Sith. In Krayt's order, there are far more than two, meaning that these are not true Sith. So therefore, the end of the Sith would've had to been before that, and the last known true Sith to go was Palpatine, by the hands of Anakin. Another point, Darth Krayt is really A'sharrad Hett, so he isn't a Sith, but a Dark Jedi. So therefore, the one who brought balance to the force, at least for the movies, was indeed Darth Vader, and, as far as I can recall into the EU, he was the only one to fulfill the duties of the Chosen One.