It's important to keep clear that the Daimos isn't a kind of sorcery like Anagogic or Gnostic, it's an application of Sorcery, like the Cants of Compulsion or War-Cants. It's rarity is in part due to the fact that to work the Daimos is to embrace your own damnation, which is something most sorcerers are loath to do and why the far reaching and daring Scarlet Spires are the ones to developed it. Kellhus has then taken their work and pushed it ahead armed with his extraordinary intellect and the Metagnosis.
Could one not consider it a kind of sorcery like those two? Just based on how the glossary describes the magics.
Anagogis - A branch of sorcery.
Gnosis - The branch of sorcery once practiced by the Gnostic Schools of the Ancient North.
Aporos - Described as a lost branch of sorcery.
Psûkhe - The arcane practice of the Cishaurim, much like sorcery, but cruder in its exercise.
Daimos - The sorcery of summoning and enslaving agencies of the Outside. (And also, apparently, visiting it, per Inversions.)
If anything seems not a branch itself, I'd think it is Metagnosis, which is described as a
complication of the Gnosis rather than a different practice. The Inversions are even outlined as 'Daimotic Cants'. It even runs on a unique metaphysical principle. The Psûkhe uses passion, the Aporos is paradoxical (if I remember correctly Bakker's comments), the Anagogis is analogies, the Gnosis is abstractions, and the Daimos is to abuse the fact of souls all inhabiting one space with speech taking control of that (The Outside) right next to the physical world.