By the way, what do Barbarians actually do? They still have very little mana... but still. They consider Nature or Life skills essential, at least levels 1-2. And there's another trick. They like to carry all sorts of scrolls (they have a whole collection of them). However, these scrolls provide their effect for half the mana cost. But for a Barbarian, this is a good option... especially if it's Haste or Teleport.
I think it's not necessary for them to develop Magic skills. It's better if they have time and opportunity to develop Tactics or Scouting.

And in general, I'm okay with resistance, because there's still the Barbarian army. And my mage definitely has plenty of room to maneuver! :)