Personally if it were up to me we would stop referring to them as range physical dps ad instead just refer to them as support dps, range physical is a mouthful.

Anyways with that said the reason we make the distinction in the first place is important reguardless if they are all dps, while normally it wont matter in normal content, when it comes to high end content this makes a difference.

Melee dps is the groups main source of single target damage and is balanced as such.

Caster dps is for aoe damage, there there to help deal with groups of adds.

Range physical dps is for party support.

Its important to understand range dps are difficult to balance because how important having extra resources can be (its why it is the role always desired to have at least one of.) By adding a third range dps they can now get a better idea of how they wish to balance this role in parties.