MCH and Monk - Why is underplayed?

[Mahrze]

I'm searching for a new main job. I thought about tank / healer too, but it must be hard for solo quest.

Allow me to enlighten you. Tanks and healers are very strong and have considerable DPS to solo quests the damage potential they lose (hardly any, brutal honesty here) is easily and considerably outweighed by mitigation and healing (tanks and healers have both of these at varying degrees at late game).