Everything has to do with:
1. Level
2. Items
3. Whats socketed in your items
4. What stat point
5. What skill point
6. What charms

You can't judge one class by just dueling 1 level 82 whatever with your super pimped out level 99 whatever and saying it sucked... It depends on the skill of the maker, im pretty sure an assassin with the right 1-6 could easy take down necro, pally, druid, zon, or sorc.... not barb though, barb 0wnz assassin....
the same goes for all the other class's, the right 1-6 can make your character excel farther than anyones every before... But you can't beat the barb at a melee attack, unless its barb vs. barb because of damn wirlwind... anyways thats just my two cents...

Peace