Storm Magic is so weak(you said week) in accuracy because it is the most powerful school. Another example is ice has the most health but it has the weakest spells. You have something good you have to sacrifice and take something bad.
I would just like to point out that by the time you reach Legendary a storm wizard can in fact reach 100% accuracy with the correct combo of gear and/or pets.
At lower levels you can boost your accuracy with Accuracy treasure cards (Keen Eyes, Accurate, Sniper etc).
