Arrow storm a little sucks deeper in the crawl, especially in the Dark Temple where is usually fairly easy to duck around a corner or step out of range, and then that ranged attacker is incapacitated by it's own "buff". Even worse when I can shoot around corners with spells, or have Perfect Aim.
I think the point of this is allowing every-other-turn shooters to shoot every turn, and so turning up their action economy. Maybe in the upper dungeon the "and can't move" makes sense, so there is some limitation to their buff.
But perhaps it would be better (for those) for them to have the buff until they move, and that the cool-down would count from when the ability ends instead of when the ability starts. (If it currently lasts five turns, and has a ten turn cool down, it would become a five turn cool down after it drops.) (And perhaps similar for other range abilities that lock movement like Sniper.)
But even that is weak for deeper down, since you can cancel their ability by making them have to move to shoot you. So, these guys should have a strafe option, where they can move and shoot. This also turns up their action economy, since if you're kiting them from the limit of range, they can catch up and shoot you. (Like Centaurs, but without being fast.) Or have Perfect Aim, so they can shoot past their melee allies. (Or have both, but only one can activate at a time.)