Firstly- You did a great job finding and comparing facts,friend!
Secondly- i'm fully at your side.
Darh Vitiate is the most powerful Sith ever lived.Sidious is just film-puppet,made for representing THE GREATEST EVIL IN THE GALAXY ,cause the Saga really was needed in Powerful Bad Guy.
I dont know was it mentioned or not, but Hero of Tython just destroyed The Voice of Emperor,not himself.you can learn about this in Sith Warrior Storyline and some fan-sites. Yep,i really didnt read all of 10pages of disputes, but im curious what happened with The Emperor after that? No explanation or something? He just gone for 3000 years?Or did he realy die sometime?