The T-V war is set in Freespace universe in which the Shivans DIDNT arrive. What would happen in that case is for the campaign author to decide. I don't see why after 14 years of war one would decide NOT to build a strong escort/fire support ship - a corvette.
If you look at WW2 - you had torpedo boats, destroyers, frigates, cruisers(light/heavy), battleships(light/heavy), carriers(light/heavy/support), submarines, etc... - note that the light/heavy versions were _MUCH different, practicly a different class.
ABOUT THE TURRETS - I know, that's why I made my own Main gun weapons
(Light, Medium and Heavy Ion Cannon, Fury MK IV, Judgment Day and Deliberator missiles) - for capships
(Vulcan, Vindicator, LIFC, - fighter guns