Clan or Role doesn’t really matter. Any clan and any role is good for bossing. As long as you have good enough gear to last through a boss fight. Some boss may be weakest to CK and some boss may be weaker to Physical attacks, so essentially hybrid is a good one to cover both Phys and CK.
Hybrid, any clan. They have a debuff skill to make sure you are able to leech HP/VE. Without this hybrid debuff skill: 1) once you hit the boss below 7HP you will become unable to leech HP/VE, hence will need to spam HP and VE pills....even so you might die many times (if not top geared) before killing the boss. 2) Sometimes when the boss hits 2HP, it will regenerate back to 7HP...making your fight longer and painful. 3) Pick hybrid for farming KL bosses