Originally posted by Angelalex242
Doesn't matter who you add to to the Sith. Even adding Valkorion wouldn't stop Full Potential Anakin.
Full potential Anakin Skywalker is massively overrated. There is no concrete proof that he forced both Son and Daughter to their knees with his personal strength and/or could do that for long. Anakin likely achieved this by drawing on the power of Mortis and/or assistance from the Father.
Father created Mortis to contain Son and Daughter and prevent their escape. Anybody who could draw on the power of Mortis, could take the place of Father. Anakin passed this TEST.