Did he actually create that dimension or just take Geralt to it? He says "my world, my rules" but does that doesn't seem like conformation as lots of characters say that they have power over or control areas when they actually don't like how Superboy Prime said "welcome to my unvierse" without being 3-A and how Ozai stated that he had "all the power in the world" and he isn't High 6-A
He clapped and then Geralt was suddenly in a different place,why would we assume that he only ruled it?He created the dimension including everything inside it,like stars,swords,monsters and other treasures.And his quote may be used as the justification.
Gaunter could just originate from different plane of existence. However, the whole place had certain theme related to the mystery he wanted Geralt to solve. Given how it ended it wasn't presumably prepraed too good. The mirrors were moving at the end if Geralt choose wrong patch and I do not really see Gaunter manually preparing certain place, placing all the mirrors and planting all the trees and breeding monsters. As for Artorius Vigo fablebook it's illusion.Very powerfull one but still illusion. Preumably placed in another plane of existence rather than created as new pocket dimmension, given that mages need Genies as slaves just to reach Montain Level. Think of it as Keira Metz mini dimmension with jacuzzi and copulationg bunnies, just made by Illusion Specialist Mage (from a family known for the illusions) rather than Mage that is not specialized on illusions. If I remember correctly Stegebor could change is Tower into garden with ilusionary fruits and people (who did not existed really but could be intercacted with (eaten/ touched). However the fact that Artorius could do the whole illusion just for two girls to play, as something like a birthday gift screams that he could easily weaponize his illusions on much greater scale unless it required tons of preparation (given how magic in Witcher works I'd say its possible)
Returning to the Gaunter it's also many times said that he is Evil Incarnate and that he cannot be defeated. Maybe he could be considered a Embodiment of Concept (Evil in his case most likely)
Well the ribbon was not an illusion spell- it was protection spell that teleported owner to fable word whatever able world is. The fact that he created sentient illusions that coud exist even without his consciouness and probably even after his death. I really doubt he just made it in random place- teleporting two ducal princesses (or whatever you would call heirs to the duchess title). Indeed Artorious is much more proficent ilussionist that what Keira or Stegebor shown, he is at least several levels above them in terms of quality of illusion. Problem is that Geralt could be killed by illusions. Is that because when he enters the fable world he becomes technically an illusion that is as real as them or it's something completly different. Given ow Witcher verse works I would never think that Artorious coud create dimmension and thencreate sentient life there, it would be far above anything sans Gaunter in verse and do not forget he was considered a powerfull wizard, but just powerfull, not the most powerfull, and Vilgenfort- strongest human mage (while very strong) was nowhere near that level.
"4-dimensional power that is shown as completely qualitatively superior to 3-Dimensional beings, but is less than universal in scale. Or that allows them to create large parts of a universal continuum."
If such a high rating would strongly contradict their otherwise established power level we cannot apply it.