ARC Auto-attack = Ranged attack..

[Akuun]

The animation of Light Shot prevents you from moving, making Archer a worthless class to bring in any fight where you need to be ready to move in order to stay alive.

Have you played Lancer in the Ifrit fight? Doomspike has a long animation lock, much much longer than a light shot.
Any class is viable in the fight, it's all a matter of the player learning to hold back on using that next action.
The fight is about survival, not DPS zerging.