Also. This is how I could see an Archer Tanking.
1. Archer Equips Paladin Job role. with the Job Role Active he has access to Job Specific Armor that enhances his defense and further defines him as being a Paladin.
2. Archer Uses hate control and movement restricting abilities to prevent the monster from moving away from him or targeting another party member.
3. In a Pinch the Archer can cast Cures from Paladin to heal himself or party members also increasing his enmity and maintaining his hate.
The downside and balance is that Because the HP and MP are based on the Weapon Class equipped Archer doesn't have the same HP or MP as a Gladiator/Paladin or a Conjurer/Paladin.
He makes up for it by keeping the monster locked in place with movement restricting bow abilities and then stepping out of range of the monsters melee attacks.