Viajero is spot on with the TTK and short time on target.
I was a multi-crew bomber pilot in Planetside 2, which I also used for Air-to-Air combat.
Old 3 minute video for reference:
Not quite 6DoF, but all aircraft were VTOLs and specifically fighters had strong vertical thrusters which made strafing fights and dodging standard for fighters. The aircraft were quite maneuverable (my bomber in the video has a boost/afterburner loadout!) and the TTK was extremely low.
For example: The belly gunner could 1-shot fighters and 2-shot other bombers.
The time-on-target only gets worse the more turrets you have — and the number of turrets you can stick on ships in Elite or Star Citizen, could result in putting
SEVERAL gunners in "the boring seats".
This was a massive problem for the guys I played with in Planetside 2. My bomber had two gunners (+fixed nosegun for the pilot), but in a 1 aircraft vs. 1 aircraft fight, only one of them would have a perfectly clear angle to shot. The same even applied to bombing runs, but the fixed the tailgunner angle in later patches.
The most fun multi-crew battles was when everyone on board could shoot at something and get kills from doing so.
I think Elite went the right direction by giving 1 gunner control over all turrets but the TTK problem remains, the interface is horrible and the gunner can only shoot at 1 target at any given time, despite having potential control over half a dozen turrets.
What little multi-crew I played of Star Citizen, out of trying the Superhornet, Retaliator and Constellation — the Superhornet was the most fun because both me and my gunner could focus one target, or split our attention.