So are light cruisers and destroyers just completely worthless outside of submarine battles and expeditions? I've got two of them upgraded to Kai but they still miss everything and when they actually hit they do 5 damage.
Meanwhile my Kongous double everything with 70+ crits. I feel like just filling my first fleet with them.
They consume more but that's the only downside I can think of.
If you go the battleship route, be advised that it will be VERY Costly!
Yeah Battleships have the best firepower in the game and make waste to the Abyss Fleets but the they also have the highest fuel and ammo consumption and if they get damaged, ridiculously high repair time and costs (ranging from 400-500+ steel for most BBs if they're severely damaged) You want to use BBs if you want an edge in combat.
Now about Destoyers and Light Cruisers, while the statements you said are true regarding destoyers and light cruisers. There are a few more things I'll point out:
As Desu-cake mentioned, Kitakami, Ooi and Kiso are pretty vital, since they can be remoddled into Torpedo Cruisers. Torpedo Cruisers are pretty much devastating powerhouses due to thier very high torpedo stats. If you managed to acquire a midget sub (hint: Train Chiyoda / Chitose to level 15, they come with those by then) you can equip them to those three and they'll be able to launch a pre-emptive Torpedo Salvo. A great method of crippling or taking out a part of the enemy forces. They use to be the kings of the battlefeild till the seaplane update, but even then, they're still notable none the less.
Also mentioned there is a map that you have to complete with ONLY destroyers. And it's an endurance challenge more or less since it involves managing to make it past one fleet consisting of a battleship before the boss node. As you'll probably learn, it's not about winning those battles there as much as it's about surviving against the odds before you so you can advance (and then beating the boss node).
And yeah when it comes to destoyers and light cruisers you have the look at the whole picture with them.
Yes they don't have the best fire power in thw world and can only do "tink" damage to battleships, and yes they can fight subs and are cost efficient. But there are two other notable points with them:
They are great for night battles and they are notably agile during day battles. Thanks to the way night battles are calculated, DD and CL can usually do insane damage. Since the damage is dependent on thier firepower + torpedo damage combined. If you know how to set up your equipment you should be able to (with some "luck") perform a cut in and do insane damage or double attack which is also damaging.
And during the day they are notable for evading shots most of the time (especially when highly trained)
But yes as Desu-cake mentioned, not all destoyers are equal, so you need to learn what they are good for so you can decide which ones are best for what.
Most of the rare destoyers and kai two destoyers are notable for being very good to use in combat:
Yuudachi: Great Firepower for destroyer, she can generally take out light cruiser and severly damage heavy cruisers with ease.
Shigure: High luck good for cutin in night battle.
Ayanami: She's basically a cross between Shigure and Yuudachi in terms of stats, you'll need to decide which path you want to take her in this case.
Shimakaze: Extremely fast, in long term training but is also slightly more expensive to maintain.
Verniy: Not as notable compared to the others, except for her ASW stats, makes her useful for 1-5
Yukikaze: Highest base luck among all the destoyers, she's almost garunteed a cut-in in night battles.
(I'd speak about Amatsukaze too, but chance are you didn't come during the Spring Event)
Some destoyers are very useful for expiditions:
Mutsuki class: Cheapest resources consumption of all destoyers. They're also very weak in combat, so they are better to use for here. (Yayoi and Uzuki might be a slight exception) (Extra Note: There will be a quest later on where you will have to use some members of the Mutuski class to complete it, be prepared for those)
As for Light Cruisers, most of them that get kai 2 or are rare are notably better in combat.
Naka Easiest to reach kai 2, decent stats allowing her to be useful for useful for various things.
Jintsuu Best for combat among the LC family, most paticularly firepower and torpedos. Also come with searchlight (VERY USEFUL in night battles)
Sendai You want to train her mainly for her equipment (which are all night battle useful gear) she's about equal to Naka
Isuzu Stongest ASW and AA ship in the team.
Yuubari While she more frail compared to most LC, she notable for having 4 equip slots, making her very useful for various things. She's mostly notable for being very customizable for multiple uses which can range from ship combat, sub combat (perffered), and
barrel packmuleKitakami, Ooi, and Kiso: Torpedo Cruisers, nuff said, I explained it at the top.
Also if you go out of your way and try to get the German Kanmusu, remember this:
PUT A LOCK ON Z1!
If you don't and remove her from your collection, you are also removing your chances of obtaining foreign kanmusus, she is VITAL for this. So do not lose her if you choose to get her from the long 8-day expedition quest run.