Ships

This has more to do with the nature of surface vessels in general. Physics demands that naval ships use lighter materials, which means fewer armaments and weaker armor. Surface vessels get detected from every angle, get shot at from EVERY direction, have no terrain to abuse, and have no resources to capture. It's simply a terrible place to be, which is probably why you don't see real animals that live explicitly on the water's surface. Everything worth a damn goes over or under in a big way.

Water combat is far more interesting under the sea. You can add seabed features like ridges, canyons, and lava banks. The floor could be rich with metal deposits or geothermal power, and may even have scraps of lost civilization. Dirt and pollution offer effective ways to hide units from detection. Bots can utilize the floor to construct bases or to build torpedo platforms. The best part is that an enormous number of things can't touch you. Most land units can't enter, and most aircraft can't even approach. Water gets to play on its own terms.

I too like amphibious seafloor combat and how seafloor relief plays into that.

What if carriers were used to somehow transport aircraft to different planets? If carriers were some kind of "airships" (or sumthing) that could travel through space to other planets or teleport around. This would give them a reason to be used as carriers.

the main value of carriers isn't that planes use them to move - it's that planes use them for logistics. carriers do carry, they carry pilots, fuel, parts and engineers as well as provide a central hub for coordination, analogous to airport control towers.

their value in PA should be the same, dealing with aircraft logistics.

Yea but ships are floating buildings. I mean, the whole rule of displacement makes that you could bring massive weapons and entire factories into the battlefield on the water.

A ship doesn't need to be light or use light materials. It just needs to displace more water than its' weight to stay afloat.
You just need a hull and a little propeller to move an enormous steel barrel. No messing around with tracks, wheels or air-cushions.
There is a reason why the heaviest armament can be found on ships IRL.

I really hope carriers are not like TA (ie, mainly a power plant) and SupCom (ie, inconvenient storage). I want carriers to be a naval superweapon (ie, expensive and kinda OP). I think carriers should use aircraft as a weapon, just like any of the other ships use torpedoes and guns. Bunch of subs detected? Launch torpedo bombers. Getting nailed by shoreline arty? Scramble the bombers. Torpedo planes coming in for your battlegroup? Launch the fighters. Carriers then become an all purpose bombardment platform, AA ship, and anti-sub ship all in one. Provided that you have the planes, that is. All launched automatically to defend the carrier and the fleet. The player can use the ship as staging bombers and repairing patrols for aircraft when needed also.

Ships in PA don't have to have the traditional roles, either. I'd like to see carriers launch troop landers and amphibious tanks for shore assaults as well. This is another area that isn't so great in OTA and SupCom. Maybe arm carriers with unit cannons? Launch planes with unit cannons maybe?