With LWAMI 3.xx, I'd say that the FFG with its two helos and any submarine are a fair match provided the mission designer starts the platforms at least 20-25nm away MINIMUM or the acoustic condition and terrain are significant factors on lowering the ranges at which engagement occurs.

If the FFG is part of a SAG with anti-missile capable ships nearby, the FFG is at a significant advantage... add the presence of a P-3C or AI ASW aircraft told to do something useful and the chances of submarine survival drop to under 20% until engagement and essentially zero after.