But they don't fulfill the same role in anything higher. Party composition is 2 tanks/ 2 healers / 2 melee / 1 physical range / 1 magical range. And yes, your party suffers if you change that composition (3 melee particularly doesn't work). Considering the breakdown of 3 tanks / 3 healers / 4 melee / 2 physical ranged / 3 casters, it makes sense why they would want to make dancer physical ranged. Oh and I'm not just speculating, that is literally the reasoning that the devs gave as to why Dancer is the way it is.
Theres a reason for that, melee physical and ranged physical healers aren't a thing, and is something you just made up. Healers are Healers. Ranged physical DPS, Caster DPS, and melee DPS are all designed very differently and do perform different roles that mostly require that role to be taken in order to be competent.