The Destroyers are blatantly broken. They have more raw firepower than any other ship, and can cripple enemy ships even at extreme range - they are more threatening from 8-10K than Long Range Frigates are! Built for close quarters brawling, nothing will stand against them. Built for sniping, nothing will ever reach them.
Combined with this is their phenomenal survivability. Destroyers simply cannot be engaged 1 on 1 by any other ship class. Even a specially built destroyer-killer will only be a match to a poorly built and badly piloted Destroyer. Only by getting multiple ships focus firing onto the Destroyer can you hope to beat one, and even then you really need either a Plasma Arc Cov-Ops, Anomaly spamming Guard or both to be piling on the dakka.
So what happens when two or three destroyers show up? You lose, of course! The game doesn’t require destroyers to be countered anymore, and I’ve seen several matches where one side has no destroyers at all because people chose not to spawn in them.
The intended balance method - destroyer vs destroyer, is not only a fundamentally stupid idea, not only broken because players aren’t forced to do it, but the devs stopped enforcing it themselves.
So we need to destroy the destroyer. Either it becomes a raw tank, able to soak up damage but lacking in firepower (meaning it relies exclusively on pyro beams and tempests for the bulk of its damage), or it becomes a glass cannon that cannot engage in close quarters and must hold at extreme range to survive.
Either of these would balance the class. But it can’t be both at once.