Hi!
The Allies began deploying a lot of new technology in 1943, such as better sonar, centimetric radar, "hedgehog" mortars, etc., that forced Germany to temporarily withdraw its submarines from action, so another way to give submarines a better chance could be to start destroyers with no advantage against submarines, but allow players to research "Improved antisubmarine warfare (ASW) technology" later in the war. so that any destroyer that entered port after it was developed would receive an "improved ASW" attribute which would give the current ASW bonus.
Just a thought....
Yes, it was what i was reading too and thought it would be kind of like you are suggesting if they have a promotion that they are weaker. Also i think they are over mobile, it looks like big battleships had a top speed of 28-30 knots while destroyers 35-38 knots... the difference in game is 4 versus 8 moves. But of course subs are more mobile too than in reality in compared to battleships.
Played with that promo on destroyers and cruisers... cruisers gets underpowered and too vulnerable to sub attacks, looks like it's better to just do something with destroyers
one thing would be to do upgrades like on land units and define different destroyer classes but that's lots of work again, not with defining those units but graphics and all that
but let's wait and see if ignore ZOC can be implemented again, it would make a difference