So I agree, the communications officer is an officer of the line and there is a lot more going on that we don't see. She's like swan, serene on the surface but coordinating a lot of people . She also coordinates damage control teams in conjunction with the operations station on the bridge.
I'm reminded of David Gerrold's quote regarding Uhura when he was interviewed for the documentary 'Building The Enterprise':
"She's the most important person on the ship. When Uhura says 'Captain', *everyone* turns to look at her."
Uhura's functional role as a member of the cast of characters was criminally under-used. But in terms of her role on the Enterprise in-universe, she was arguably one of the most crucial officers aboard.