Destroyers are with the CV task group for historical reasons and for mutual defense. Everything in this game like a task group, PT, LVT or tigerII is dictated to their effectiveness by time, distance, and everything from 30cal to 1000lb bombs.
We all know how long lone CV, Cruisers, destroyers, PT, LVT, and tanks last after some kiddi with 1000lb bombs finds them. We also know because of the scale of our game world the PT, LVT, and tank has to be spawned to it's combat area which is a very tiny operational space, often less than 2x2 miles versus the ability of those conveyances to get there in one evening directly from another base. Time, distance, and 1000lb bombs.
Where do you want to spawn a single destroyer to? Airplanes with bombs will take out a single destroyer as so cruiser 8in batteries out side of the max range of 5in and torpedoes. Massed 5in from the task force will take out a single destroyer. And shore batteries will, just like taking out PT, LVT and even tanks. Tanks have a few advantages for hiding up to a point that sea craft do not.
It's not like you don't have destroyers in the game with guns you can man. You will get an entirely new battleship object in AH3 with 16in guns that good chances will be the heart of it's own task group with destroyers. I've tested the salvo and it only takes three to sink a carrier with a longer reach than the 8in.
How are you going to bring a single destroyer near anything to fight and even survive against in a world that would swallow up the standard arenas of our competitors? Instead of punting it onto Hitech at this point, use the game functions as we are familiar with them to conceptualize this outside of a member of a task force. Where do you want to spawn a single destroyer to that it won't get sunk after it is located? This game is not world of warships protected from planes, it is Aces High an air combat game with task force sinking experts once they are located.