There currently is no viable naval counter for sera vs cybran t2 subs on naval. sera destroyers have horrible torpedo defense, range, and torpedo damage. So if the cybran player masses t2 subs (1.1k mass) vs sera destroyers (2.25k mass) they have a hard counter for half the mass. t1 subs cant do any damage to t2 subs.
This leaves 2 basic options, torpedo bombers, or outplay them so badly that you can tech up to t3 and make t3 subs. with the nerf to torpedo bombers, and the fact that if they land in the water they wont hit the subs, this leaves a massive exploit.
a possible solution to this could be increasing the reloading time of the t2 sub flare, or decreases how many torpedoes it fires so the sera destroyer has higher survivability. As soon as there are 4-5 subs, not a single torpedo can penetrate their defense, and if they do, its minimal damage.