OKAY
I've managed to successfully figure out how to manage myself, at least in a Normal difficulty game. The answer to most of the vanilla stuff I've encountered so far seems to be 'fly real high and spam bombs'.
I've run into some unpleasant AIs who prescribe to the same idea. I had a tough time with one of their shipyard cities that had like 6-7 tough defense towers with rockets and flak guns, but after massing enough bombers and bringing in some tanks that could negate those annoying flaks I managed to break them. All the while they kept raiding the little towns nearby - even after spamming piles of 0 maintenance tinydefenses around equipped with deck guns, dorsal turrets, flaks, and beefy stone armor as I was able to research stuff up, it was still kinda a crapshoot to deal with them, as the bombs could usually disable the weapons, or they'd just eventually run out of ammo or whatever, even though the enemy ships were decently fragile and prone to chain explosions.
So far I've run into the same issue of 'The AI tends to surrender shipless provinces a lot' that I saw someone mention earlier, and it has been kinda aggravating that I haven't been able to see how effective the newer designs have been since they roll in numbers apparently too scary for the AI to deal with, but on the other hand it's probably good that I don't have to sit through 3 huge heavy tanks blowing away 1-2 rifle towers with every expansion.
I'm considering some mods, but I'm not sure I like the idea of rocket airships and the like, since those seem to be blatantly better than all the vanilla shit - those rocket engines for example look both smaller and are apparently way faster and such.
I've been having trouble figuring my designs still. Bomb bays have been crazy effective, and a lot of the other stuff doesn't seem quite as much so. I've tried an Imperial cannon-focused tank, but that thing seems to miss a lot, and against the 6-7 aforementioned rocket/flak towers I took 3 big rockets, but those seemed to chew through them real slow. Bombers seemed to do the job better. Some Heavy Cannon tanks seemed to miss quite a lot, too.