There are already plenty of one hit K.O. spells. They belong to the Storm and Fire school but more so to Storm. Go into the commons and look for a high level Storm person. Ask them to show you Triton, Tempest, Storm Lord, Kraken, and Storm Shark. Bladed and trapped these are all one shot kills against most enemies. Triton or Tempest properly bladed and trapped is a one shot kill against most bosses.
Now if you're talking about one shot kills for each school then I have to strongly say no. That kind of power is what makes Storm and Fire so strong. If you start to take that power and share it out amongst the other schools then you are (a) making Storm and Fire less meaningful and (b) making the schools more bland.
