-IMO each class can be just as good as each other, just have to build them to be epic badasses...
I tend to get lots of passive and sustained abilities-
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In the first game I ended up going Mage/Arcane Warrior/Blood Mage with pure magic build.....I then got any and all sustained modes that boosted armor, defense etc and built from there....ended up being an insanely powerful tank....equal damage if not more than and equal if not better tanker than a Warrior....and all this with the added perk off being able to unleash epic spells etc.
Only started playing the 2nd game a couple days ago, I went DWRogue/Shadow/Assassin because it was something I had wanted to do in the first one but didn't get around too (Maybe one day)...once again I made a somewhat passive focused character, this time aiming to inflict as many critical hits as possible once you get a few levels, some good daggers and get your specialization happening, bit by bit you become unstoppable...there were a few times where I stun-locked bosses all the while criting the hell outta them, specially late game.
Now I am slowly cruising through playing a Mage/BloodMage/which ever other one I decide, heavy focus on sustained modes.
So yeah basically it is about how you play the class, not which class you choose