I really like good sins in a party, they hardly take damage. The only thing is, not all sins are good. There's a high percentage of encountering a newbie player everyday. If that's the case, people will pick a newbie FM rather than a newbie sin. Since it takes more skill to dodge and dps the boss compared to a ranged dps. In bosses where they dont jump/move, i think sins will be on top. But if you will consider all bosses including the ones that jump, move around, any skill which melees cant do damage, FM will have more damage.