How it should be:
T1 Frigates - Fast, surface only, radar, sonar, pwned by T2 destro
T1 Subs - Fast, stealthed
T2 Destro - Slower, surface fire dogsbody, wins surface vs all, dies to T1 subs, has flares and weak torps against T2 subhunters
T2 Subhunters - Long range, high alpha, beat T1 subs, lose to T2 destro, lose badly to T1 frigate, very low HP so lose to destro.
T3 BS - Bombardment, loses to most, needs escort. Think of as T3 Mobile Arty on land
T3 Subs - nuke station, super-long-range defensible bombardment, needs escort. Think of as T2 MML
Everything else can be fit in as unique units or variations on these themes, such as the BC being a bigger destroyer.
All frigate? Pwned by destro. All destro? Pwned by T1 sub. All T1 sub? Pwned by subhunters. All subhunters? Pwned by destro. Destro + subhunters? Frigates + subs, depending on mix (Frigates go in and kill hunters, die, but subs then kill destro. Countless variations need testing, but it's better than where we are right now.