Which one is stronger?
A 12 heavens will cultivator (Tenth world) vs. a primal ancestor cultivator (Immortal world) . Which one would win?
What's primal ancestor again ?
From what i remember, cultivators in 3IW system opens a new Fate Palace with their each breakthrough. When someone reaches the "Heaven Ascending True God" realm , they can open 11 Fate Palace. After that comes "Forever Existing Immortal" realm where the cultivator opens their 12th Fate Palace. After this realm. individual power depends on the cultivator's comprehension of Grand Dao and the foundation of their Dao Heart. Like how there is the "First Ancestor" of Immortal Dao Devil Lineage who can casually crush Forever Existing Immortals with little to no effort .
But if we're comparing the strongest characters from each sides, like "Forever Existing Jiang" of 3IW against the "cold faced" Emperor(forgot his name, he's the guy who fought against the first introduced Dark Giant alongside Li Qiye), both seemed pretty even tbh
So in a way , there's no proper answer. Their combat ability depends on their own individual comprehension and Dao heart