The immobilizer-418 was supposed to have been built on a 'standard' cruiser hull, yet we never see the cruiser it was based on, just the Intereictor variant. I'm guessing those ships would have served a role much like escort frigates and the smaller 'cruisers' we've seen in rebels, only somewhat bigger. I can imagine some large gun emplacements where the gravity well generators are placed.
We do see the Vindicator in a couple of things. Not much though, also somehow the vindicator in old canon could carry 72 fighters, despite being a third the size of an Imperator.
Wait the Vindicator has appeared in canon? Where?
And regarding the Vindicator having 72 fighters in some configurations that is nothing. The class II Frigate was only one quarter the size of an Imperator but had six fighter squadrons, incredible firepower for its size and era along with defenses fitting a heavy cruiser more then a frigate, and a standard crew of almost 20,000 personnel, with Dreadnaughts being fifty percent larger and considered to have a very high crew to size ration with a standard crew of 16,000, plus a hyperdrive that was only rated for half the speed of standard warships in the Imperial era. I'm still trying to figure out how and why the Empire approved the design for production and what the WOTC approval board were high on the day they approved the statblock.