Naval has amounted to sub spam.

Ah they changed that then

About the price and performance of battleship, I think you over underestimate them.
First, the price isn't that expensive as you think in the middle game since you will expand and glow your eco.
Second, the battleship has the area of effect which can knock out a group of walls very quickly.
And the torpedo launcher won't survive too long.

I originally think you are talking about the Pacific or Meso.
As you say that there are 3 1vs1 map with narrow water, I think you mean the Amplus and Clutch.
In my opinion, the torpedo launcher isn't the problem in both map.

For Amplus, the river is small.
The navel units can only fire to nearby region.
Though the navels can clear out the starting location of the enemy.
The enemy may just move to the area which is away from the water.
You still need to use land units to attack the enemy.
The air units is also the key in this map since this planet is quite large.
Lock down the river by torpedo launcher won't make too significant effect.
The opponent can also makes some torpedo launchers, and add few pelters to out range them.
Or just bypass them using land force.

For Clutch, the major problem isn't the torpedor launcher but the navel unit itself.
Once enemy build the navel units in the water, it is very difficult to dig them out
because the navel units are stronger than land units.
I usually build the navel factory after I build the metal extractors on the island.
After building few navels, I often make the the battleship to attack the enemy base.
The opponent usually gives up when they get arty by battleship.
The method to prevent this is to scout the water region of north and south pole often,
don't let the enemy air fabricator to build that.
Or just win the land battle faster.
But I think the best way to counter this is to make the navel factory of your own.

If someone is spamming nothing but Torpedo Launchers then you'd counter with Drifters. Or Bumblebees. And mobile units will always have the edge because you can focus your entire army in one spot, while their Torpedo Launchers are spread out.

Torpedo Launchers are strong and a key part of naval play (more so than turrets are land play), but OP? I don't think so.

Bombers aren't effective because their bombs are spread out far too much and do little to no damage on subs.

Build torp launchers on land, adv torp launchers, hover units and air all counter subs hard.

There are strong but certainly not the only unit I would use.

Well, hover units can take out the torpedo launcher.
But they can't counter submarine since they lack the torpedo weapons.
Submarine are immune to water surface fire.

Similarly submarines can't take out hovers, so makes it difficult to defend sea expansions if you spam submarines only.