There is a bug I belive. Spells or weapon bonus are bugged. They should work same way.
All spell should add bonus only to the spells of their own school. Same as weapon skills does.

If you want to add a spell bonus to any actions (like life leaching necro-rogue now), then weapons are bugged. Because you need to add accuracy to all action if you get one handed.

I believe in consistency.
Weapon skill or Spell skill bonus should behave the same way. In my book, the weapon bonuses works correctly now, so spells should fallow.

When you are Pyro, then getting better in Pyro your spells are more hot. Eventually, on level 5 you are so hot so you can take Deamon. All your skills are related to your study in Pyro spells.

Same way Two handed weapons or Necromancy. You spend your time on taking skill in the area. So big weapons are deadly on level 5 skill but, If you take a food-fork you can not apply two handed weapon skill. Same as if you stab someone then doesn't help you know how to rise dead.