You can make scoundrels and huntsmen who deal more damage than warfare builds, but absolutely not magic users.

Its simply because physical does not have resistances and magic does. Most enemies from Act 2 on have multiple resistances, and very rarely a elemental weakness. So while a physical character is dealing 500 damage every hit, your magic user is hitting 500 damage minus elemental protections.

This doesnt really matter though. The game is easy and you wont be challenged even if you make a sub-optimal build.