Whether it's the original novel or the TV series, the world of "Journey to the West" emphasizes Divine Skills more than realms.
There's no mention of Foundation Establishment, Golden Core, or Nascent Soul at all!
These elements are modern fantasy constructs and can't be applied here.
So, the question arises, what level would Sun Wukong be if we tried to apply a familiar power system to him?
This is where it gets messy, with nothing to compare.
Now, as the comparison started, Li Xu realized that he was totally powerless as soon as his Fiery Eyes and Golden Gaze fixed on him, with a sense of helplessness and weakness engulfing him amidst the crisis. He yelled, "Elder, save me!"
The scene blurred before Tang Sanzang's eyes, and Sun Wukong had already vanished. Remembering the ambush Li Xu had set up on the mountaintop, he urgently shouted, "Stop!"
Had that shout been a second later, Li Xu's head would have been smashed by Monkey Fist.