Well in the movies we see shots coming from all over, but the overall rate of fire isn't that high. Maybe they've got tons of firing points but they deliberately stagger their fire? Or are somehow forced to stagger their fire, even... perhaps a combination of whole-ship energy concerns and per-turret reload/rearm/chargeup/whatever?
^ This is of course just one possible explanation, which could explain the big numbers of turrets, versus the small amount of fire actually seen... and would allow the game to be actually playable. Although it'd still be kinda funny having all those turrets being idle most of the time, and I don't know if that'd be doable in-engine...