Vitiate > Soa confirmed.
The great evil sitting at the center of the Eternity Vault is a Force-using Rakata warlord who once brought Korriban to its knees. Now the despot known as "the Infernal One" intends to conquer a galaxy that has forgotten him.
―Star Wars: The Old Republic Encyclopedia
Soa is confirmed to be a dark side Force-using Rakata.
Vitiate however is confirmed in the same source to be the most powerful dark side master, and most powerful Force-user in the history of the Old Republic:
The Sith Emperor, history's most powerful dark side master.
- Star Wars: The Old Republic: Encyclopedia
The Sith Emperor is the most powerful Force-user who has ever existed. Unless this implacable enemy can be defeated, the Jedi Order is doomed.
- Star Wars: The Old Republic: Encyclopedia
This is incredible given the breadth of Soa's power:
The Rakata kept most of their prisoners alive on purpose. The Eternity Vault was for the ones they couldn't kill.
― Star Wars: The Old Republic
The Rakata civilization was powerful beyond measure; the threats they sought to contain in this prison transcended anything the Republic is currently prepared to face.
―Star Wars: The Old Republic Encyclopedia
"The Rakata known as the Infernal One is a being of terrifying power."
―Star Wars: The Old Republic Encyclopedia
an ancient and deadly evil that could threaten the galaxy.
- Star Wars The Old Republic Official Website
Keep in mind just how powerful the Rakata were at the pinnacle of their Infinite Empire. Ajunta Pall has stated that the source of his, and his fellow Exiles' power, was the Star Map:
"We were not the first to fall to the dark side. But we had more power than those before us. It came from elsewhere - our oldest secret. Only we would know, we lords. Only we would know where our power came from. It is a secret of so long ago. I no longer remember. So much power, it is blinding. You must find this place, or have you? Or did you? Or will you? Oh, so many images. I see your heart, human Jedi. I see your power, your pride. You, you will find the old place, the dark place, and you will regret it."
―Ajunta Pall
So the Jedi Exiles were drawing power from this source of energy, meaning it had made the likes of Karness Muur so powerful as to be a near equal with the likes of Darth Krayt.
Yet this source of power was a mere Star Map, which is effectively a mobile phone compared to a nuclear reactor of a Star Forge or Foundry. Despite all of this power, the Rakata were incapable of actually killing Soa. They settled for sealing him within the Eternity Vault, which draws power directly from hyperspace, and could've destroyed numerous star systems if it was overwhelmed.
Soa's own feats are in fact incredible, tearing apart numerous fifty foot statues without gesturing, and launching them with enough force that they destroy part of the massive cage designed to be invincible, whilst said cage is holding him:
Yet not only is Vitiate more powerful than him, Valkorion would be far more so:
With each rebirth, he grew stronger. His machinations became grander. The pain and suffering he unleashed became greater. Some believed his ultimate goal was conquest: the complete subjugation of every world, known and unknown. Others believed he sought annihilation: the consumption of every living being in the galaxy, until he alone remained.
- Star Wars The Old Republic: Knights of the Eternal Thrones