Akasha is the Universe itself and it is Omnipotent in its own Universe. Effortlessly triumphant against other cosmological entities or servants who lives in its universe. It's more powerful than any Archetypes and It's the source of Void Shiki's powers.
But if the concept of Nasuverse is like Marvelverse, which an Omniverse that consists infinite number of Multiverse exists, then Akasha might be omnipotent in just one-dimensional scale.
And If its so, then I would bet my pride on The Primordial Goddess or Ashtart Origin as the most powerful being in Nasuverse. Her power would be on par with Akasha, IF her Origin Universe might had come from outside The Universe of the Root, thus, making her omnipotent in her own right, She might rival Akasha in terms of power. She's the oldest, and the original universe before the update happened, it was completely replaced by new ones—Servant verse which is in Nasuverse a.k.a The universe of Akasha.