What it's saying is that unless you are attacking a specific people there's no way I'd ever play a Thief or a Gunner. Both have two classes that own them and everyone else does normal damage. Warrior and Mage are both very defensive as they only have normal or weak attacks against them. Actually a fight between a Warrior and a Mage would be fruitless as they are both weak against each other.
Really the only balanced class is the Hunter.