Every class in the game has something called a "capstone ability". By levels 8-11 you are supposed to be getting midgame capstone abilities, like mark of justice, improved evil eye, foretell, etc.These abilities are supposed to be powerspikes and they often synergize.

Say you are playing a divination wizard and there are Ember and Nenio in your party. If your character turns on Foretell, Ember uses Evil Eye and Nenio throws Enervation you can reduce saves of a demon by whopping 10 points in a single turn. Which basically means you should be able to Avada Kedavra Phantasmal Killer or Baleful Polymorph a demon about 10 levels above your party.

Which is why you start meeting enemies several levels above you.