I read your posts and played a few more games. Here's what I came up with as of now.
Whirlwind Light Gatling Gun: Want to kill a ship? Damage the hull! Want to damage the hull? Use this weapon. It’s the best for breaking that all important barrier, and it breaks a lot of other things too such as guns and engines.
Hellhound Heavy Twin Carronade: This weapon is so popular, it has an entire build named after it called the ‘Blenderfish’. Pop a balloon, and kill a ship. This single weapon is a complete strategy, and dang is it annoying to go up against!
Scylla Double-barreled Mortar: Break ships with stripped hulls at short range. Little use for anything else, but that’s a pretty important thing to do!
Barking Dog Light Cannonade: Yeah I can admit when I’m wrong. A balloon popper is not fun to fight against. Pair that with a flamethrower and now you’re just being mean. It does have a very short range though, so it has a specific role.
Dragon Tongue Light Flamethrower: If batman were chemspray this weapon would be the joker. Still, it remains quite popular as it can overwhelm enemies with persistence. A solid close range option for speedy ships that can afford the risk, or larger ships that want to give speedy ships something to think about!
Banshee Light Rocket Carousel: A longer ranged slightly less effective flamethrower. Want to send engineers running and give them something to do? Pelt an enemy ship with some of these. Not bad against stripped hulls either. A persistent stream of rockets will eventually disable and kill a ship. Recoil issues prevent extreme range use without heavy clip.
Artemis Light Rocket Launcher: Hull damage and explosive damage in the same weapon. Enough of them (say 2 or 3) is capable of killing ships, if you are patient enough. Wide firing arc permits many different applications.
Hades Light Cannon: If you can hit with it, you should use it. It’s better against larger ships because it is difficult to aim. A consistent volley will put any ship it bad shape though, removing its armor and setting it on fire.
Manticore Heavy Hwacha: You better Hwatch yourself! One barrage from this weapon can disable an entire flank of a ship’s guns and engines. A good finisher with enough persistence.
Echidna Light Flack Gun: This weapon is only good as a long ranged de-hulled ship killer. It must be used at range and does not have much armor damage capability. Pair it with a mercury, shoot ally ship’s targets, but whatever you do don’t expect to use it alone. Its overly specific role belies its usefulness.
Beacon Flare Gun: Once again, a useful utility. I have seen it turn the tactical situation of games by revealing a target or denying a squidfish a flanking opportunity. Is it a weapon? Some say it is. I have yet to see 2 mounted in front of a pyramiridion though.
Lumberjack Heavy Mortar: The long ranged balloon killer. Good for 3v3s or stopping enemy ships in their tracks. It’s heavy and has a narrow fire cone though. See mercury field gun.
Mercury Field Gun: While not completely useless, this weapon has a purpose which is so specific it is rarely used. A very long ranged narrow cone light hull damage weapon. Having such a specific purpose relegates this weapon to open maps of 3v3 where ships spend time in a standoff exchanging ranged volleys.
Phobos Mine launcher: I have seen people use these more often now beyond king of the hill. It actually is a good area denial tool which can knock ships off course or flat out kill them by shooting down on them. Takes a lot of practice to get the arc right which makes it less reliable, but it pays off when it works.
Typhon Heavy Flak Cannon: It’s rarely used for a reason. Hard to hit with at range and does less damage up close. Perhaps hitting targets with it is a question of skill, but there are better, more dependable weapons out there.
Javelin Light Harpoon gun: I haven’t found a sky whale yet so I haven’t found a use for this.