The True Keyblade Master

I just realized that either MX or Vanitas could have been the keyblader that tried to destroy the world. In KH I, you find out that there was a saying about the keyblade, something like 'one saved the world while another brought ruin to it'. It would serve great poetic justice if Vanitas fit this description since he is sort of the evil sora. What do you guys think?

Xemnas was the nobody of Xehanort. His heartless was Ansem SOD. My question is how come we never fought any of the other organization's heartless like Lea's(Axel) or Sai(Saix)?

while its not my favorite - which is eternal session- im surprised that no one mentioned Proud Roar(the one with simba)