Eh, debatable. Warriors do mostly damage to one enemy, which can miss. While rangers and wizards can do ridiculous damage with their elemental combos. They're also most effective blocking the enemy's way and benefit from using heavy armour which is tied in with Strength. Maybe in late game they may become stronger but then again, this is just a tutorial for those starting out. I don't quiet think they are "the main damage dealers" unless you care to prove me wrong
No it's not debatable.
A properly used Warrior can dish out more AoE and Single target than Ranger/Mage unless there are very specific conditions i.e. some environmental stuff or objects boosting damage, but they usually get destroyed once you use them.
If you had played a proper Warrior extensively you'd know, anyone here can tell you the same thing.
