This is based on some tests vs AI - please suggest updates as per own battle experience. The idea was to explore lategame counters to amphballs by ships.
Test 1 (5000 metal):
Amph build :
1 Grizzly
5 Scallop
5 Duck
2 Angler
5 Archer
Sea army 1:
10 cutter
11 Hunter
5 mistral
5 seawolf
5 corsair
- Sea army a-moved into enemy - sea loses with grizzly alive, but escort units killed.
- Sea army moved in with 3 "layers" - cutters and corsairs go first, hunters and seawolves next, with mistrals in the back. This works slightly better with grizzly dead but escorts surviving and killing all hunters and seawolves, forcing ships to retreat.
- Sea army engages with corsairs as suicidal screen, then everything else - outcome is same a before.
In most of these cases the antisub capability was destroyed decisevely, making ships vulnerable to ducks etc. Suboptimal.
Sea army 2:
11 hunter
15 seawolf
1 siren
Siren was sort of useless as it was too slow to engage. Somewhat tenuous victory for ships.
Sea army 3:
23 seawolf
17 seawolf survive, everything else is dead. Minimal micro to reduce AOE impact of archer was applied. very decisive victory for sea.
Sea army 4:
8 siren
2 hunter
4 sirens survive the battle, not as decisive as with subs but siren has more utility elsewhere.
Test 1 (20000 metal):
Amph build :
4 Grizzly
20 Scallop
4 Angler
15 Archer
10 buoy
2 limpet
Sea army 1:
20 siren
15 corsair
20 seawolf
9 sirens survive. Sirens tend to damage themselves when fighting submerged grizzly, intense micro would be needed to prevent that.
So, basically, sirens murder amphbots composition fairly decisevely if you can afford them. With income parity, ships have a somewhat convincing advantage vs amph, as one would expect.
Coming back from behind sea army 1 (20k amph vs 15k sea):
10 siren
40 seawolf
Result - decisive victory for amph with 10k left
Pure siren spam for 15k:
Result is decisive victory for ships.
In case someone is wondering why ships have no AA in the mix - that is because ships have no AA units available, of course.