From my experience in MMOs, the warrior/fighter class style tend to be the bane of Assassins; and rightly so as there needs to be a limit to their targets. Assassins have a habit of destroying rangers/archers/magic users due to the obvious ability of taking away their range before the fight begins. But with the warrior, the Assassin is attempting to fight them at their own game... only they have better armor, more hp, and generally alot more survivability. The assassin is destined to lose any form of "fair" fight here.......
But thats why Assassins dont fight fair.
