Ah, I see what the problem is.

Alar at one point made the change you did, but later deleted the file after a patch to the vanilla game. I then recloned the vanilla file during the Rahta revamp, but the localization from Alar's first variant remained intact.

... In other words, the use of vanilla balancing is intended... even though my first instinct is to agree that it's ridiculous...

Basically, the 'correct' fix is to remove the Destroyer-related localization from the mod's files rather than restoring the Destroyer changes, and the right fix right now is most likely for me to bug Alar about it. :P

With that in mind, it's off to Discord for me.

I honestly have to say that I will stick with the changes to 3x strengh now.... because the AI simple had NO chance at all. A 22M strength destroyer hull ship was able to kill a 150-200M strength ai ship with now problems. If it is only 3x and not 6x carriers make sense again and a carrier of the same size has to be surprised by the attack of the destroyer to win.

If it really intended to use the vanilla setting here building any ships beside destroyers is a plane waste and in my opinion a shame to all of the other design possibilities :(

It may be that the balancing was done around player designs rather than the inferior AI-generated stuff. Illyia is basically screaming 'this is as weak as we can afford' while Alar's saying 'it was even tougher in my original version'.

You'd have to go into the Discord chat at https://discord.gg/sUJKJDc and discuss it with them, probably in #feedback - I, for one, am now convinced that this isn't a bit of leftover balancing or anything, and that it has a purpose, so I'll leave it be.

I'll chime in here bit late but whatever.

The AI is currently not coded to be able to fight destroyers or in fact any heavy tank build. They do not utilise support ship behaviours (which are essential to prevent flagship sniping) nor do they seem to recognise what is required to floor stomp destroyers with support ships.

Basically if the AI were a player that huge fleet would most likely end up beating you, but due to how the AI is not coded to recognise, counter and also make use of essential support ship behaviours they fall down hard.

Against players destroyers normally only end up winning through attrition, staying in the fight long enough to be able to exhaust the other supplies just due to how players well utilise support ship behaviours, in this case the near essential shield behaviour to prevent/limit flagship sniping. When a player uses such behaviour a typical destroyer not stacked with at flak cannons can barely get through the first few (if the support ships are about 5%-10% of the size of the destroyer it might break through about 20-40ish of them) before enemy supplies are exhausted after a few minutes of combat. Once the enemies fleet is out of supplies thats when the still supplied Destroyer starts to sweep.

When you combine both the shield behaviour with missiles the destroyer is stomped in a minute or under with minimal casulaties to the enemy fleet apart from just needing to fall back to get some supplies from friendly space.

The AI just never does this and because of this fails massively at fighting destroyers.

I cant remember AI use this but:
File under server/empire_ai/weasel/designs
indicates that AI should use Shield and Brawler behaviours:

//Set design settings/support behavior
if(purpose == DP_Support) {
if(dsg.total(SV_SupportSupplyCapacity) > 0.01) {
DesignSettings settings;
settings.behavior = SG_Brawler;
dsg.setSettings(settings);
}
else if(dsg.totalHP > 50 * dsg.size) {
DesignSettings settings;
settings.behavior = SG_Shield;
dsg.setSettings(settings);
}
else {
DesignSettings settings;
settings.behavior = SG_Cannon;
dsg.setSettings(settings);
}

1. I dont know if AI in game uses this /weasel files.
2. I suspect that it does as I havent found other file like this one. That means that AI should use shield support behaviours.

As I said Im uncertain If Ai uses this /weasel file or other. Im tinkering with idea of improving AI designer so please direct me to relevant files if Im wrong here.

These are from empire_ai/BasicAI and empire_ai/include/bai_act_fleets
3. AI picks Hull for combat flagship totally at random.
4. AI tries to use Flagship Killer , filler and other types of supports but for example Flagship Killer is in game represented as Heavy Gunship (and always preloaded) That means that improving Heavy Gunship preloaded design should also improve AI flagkillers capability.

Has anyone saw AI building a combat station? (defense platform in game)

Edit: removed these lines at the end at it was mostly speculation
Edit2: Assuming this file is working I can put 1 instead of 50 there and Ai should use All designed support ships as shields. So there is a way to test it.
Edit3: Currently Ai is evaluating 10 "random" designs before choosing the best one, it might be forced to evaluate more at the cost of reduced game performance.

I found this in: weasel/WeaselAI
//How many potential designs are evaluated before choosing the best one
uint designEvaluateCount = 10;
//for tweaking purposes: (this value is overriden by easier difficulties further in the file, just use ctrl+f "design" to find that)