I'm playing a "mage" on normal difficulty with with maxed Willpower and Mental Power, and maxed mage skill trees. (Not in parallel, but going for Storm spell asap.)
When fighting mobs I just run just into them, cast the storm spell followed by spamming Shadow burst. When mana is depleted, in most cases all but 1 or 2 creatures are dead. I let my companions kill them or wait a bit until mana is restored and cast a few Shadow bursts. I never used a secondary weapon and don't bother having maxed out gear.
You just have to make sure that fury is filled after a battle so you can start your next one with Storm again. If it's not filled I start with some Stasis and/or Shadow burst until it is filled.
Playing like this fighting mobs is very easy.
When fighting bosses it's a little more difficult as you I can't make good use of the Storm spell. Here I need some mana potions and it might even happen that I get killed if I failed to dodge and/or was too reluctant to heal myself.
So with this really simple strategy you need to play on hard difficulty at least.