Purpose of Marksmen

[CumeriTarenes]

Regnum online is a RvR game in the first line.
Every class has unique abilities that benefit the group.

barb: gives speed and damage bonus to the group. Speed for rushing in or running away.

Knight: protects the group with auras to increase block chance and decrease received damage

hunter: can scan the area for enemies and can hide a group for an ambush

conjurer: mana and heal supporter, area dizzy of enemies, kind of energy barrier for the group

warlock: also mana supporter, can also protect group with auras to increase block chance, also kind of energy barrier of the group, several area combat control spells

marksman: just most range and death sentence? What is a marksman for? How does a marksman serves the group. Marksmen have no unique spells to help others directly. All they can do is dealing damage. Is this what marksmen are only for? I mean, there is no class that can be substituted by other classes at all. But marksman...they can be substituted quite easy by other classes.
For this my question, what is the uniqe ability that makes a marksman to a marksman.