Given how every hover and ship have sonar I'd barely call it a stealth mechanic. Unless it was expected that seas would usually be empty or that only planes would patrol them. If sonar was limited to only cutter, hunter and siren - while for hovers it'd be dagger and claymore I could agree on it being stealthy.
However I see it more as an armour mechanic, or some other sort of layer separation. While in most games we can't shoot at air, where as here we can with our flex aa. Then our lack of privileged layer had returned in form of ducks and seawolves.
