Well, I should point out this is a circular argument; there's no such thing as an uncounterable strategy, it's the timing you have to devise and implement that stratey that makes the difference.
Perseus with Trebs can be countered by escort fighters, AAAf beams or simply running diversionary attacks to draw away the destroyers fighters before an attack.
Ravana can jump in at the GTVA destroyers weak spots - front, rear, probably top or bottom - and attack there. In particular, attacking the rear to disable the destroyer, launching a defensive screen of interceptors, and them possibly raking the ship with its beams or focusing on the rear solely.
An admiral might insist on Trebuchets and escort, but you don't always get what you want in war; the Shivans might divert the escort as mentioned earlier, or cut off the supply chain of munitions.
A pariticular issue being the fighter cover of the fleet; the Shivans have a distinct advantage in having smaller fighter carrying cruisers, which means they don't need to rely on destroyers for the escort of their entire fleet.
IMO the Shivans would win, simply because they have the numbers to tie up every GTVA asset and thus manipulate the battle to their ends. I don't think the GTVA could engage the Shivans in any sort of large scale front and maintain a tactical advantage.
Thus, I think the Shivans would be in a position to use the Ravana tactically, and as a result the Ravana would be used more effectively than the Demon due to its more focused firepower.