As I see it, there are two useful ship types which should be easy enough to build that aren't listed. The first was just added to the game, namely
PT boats.
The second hasn't been, but fills a useful pseudo-auxilary role, so I'm curious if you will allow it. Specifically, I'm talking about something in the under 2000 ton, slower than 20 knots category, such as a British
Sloop, an American
Gunboat, a French
Aviso, or a Japanese
Kaibokan. This class of ship is normally both high endurance and good at anti-sub warfare. In some cases, such as the american class I linked to, they carry 6" guns, making them a potential threat to light cruisers, despite generally not having a torpedo armament. I see us using them whenever speed is
significantly less important than fuel use, such as resource gathering.
As for PT boat... Well, even as annoying and broken as they're in games, they wouldn't be very useful at the moment because of their extremely short range. There's also a hidden prerequisite before you can build them.
As for small escorts/A-S vessels... I didn't bother to put them for now because I didn't want to put many, many small vessels right from the start. And thinking about it I will keep it that way for now, no need to go too complex from the beginning. They will be available later on, though. As for their advantage compared to destroyers in resources gathering, remember that they wouldn't be able to carry as much, due to being smaller and all that.
...
Funny thing...
Even with all "can we be bad guy" going...
We can't. Because by stated facts Abyssals are hunter/scavengers. Without something to hunt/scavenge it's end.
Essentially win condition that is not mutual kill is not "kill 'em all" but "make 'em pay tribute". Which requires quite different and I must say nicer approach.
...
Well, for some "kill 'em all and die/wallow for eternity in helplessness" is win condition certainly...
Well, Abyssals are not the most rational beings. You know, resentment, hatred, grudges and all that... Quite a few would be perfectly alright with mutual annihilation.
Though the smarter ones, once they calm down a bit, realize that annihilating humanity is not something they can do. Often, it's not even their goal. But then, their objectives would often require total victory to be accepted anyway, so they decide to do that first so they can then dictate their terms.
In that, the fact that the Abyssals aren't really an united factions doesn't help. There's actually a few who will fight each other over silly things like : "You killed me!" -"You killed my sister first you bitch!" Though others make up because "it was all the humans fault anyway, let's team up and kill them". But like I said earlier, not the most rational beings, so it depends.
In your case... Well, you truly gave your best. Your service was exemplary. But all that just served to underline how pointless, hopeless the whole war was, and had been from the start. The particular circumstances of your death making that all the more obvious.
And when the humans decided to call you again to fight to for them again? Well, that pissed you off. You didn't manage to avoid getting dragged into this world, but you certainly weren't going to give them what they wanted.
At the moment, your particular objectives and goals are kind of vague, though. That's up to you (the players) to define them.