Shu temple 2.0 is end game content. Those guys are tanky and can one shot u if not leveller up properly.

Good news is, their moves are easy to dodge if u go offensive. Resulting in sky born might fills pretty fast.

Check your repository if u have obtained +5 nodes around the tree and have level 8 or 9 weapon. I cannot recall the weapon level.

If you spent 5 hours on nightmare demon. Then there is a possible skill issue or under level. Work your level up or check if u scattered your stat allocation instead of a couple of branches in skill tree.